Method and apparatus for digital watermarking

ABSTRACT

A method for embedding digital watermark data in digital data contents includes the steps of obtaining a frequency coefficient of block data of digital data contents, obtaining a complexity of the block data, obtaining an amount of transformation of the frequency coefficient from the complexity and the digital watermark data, and embedding the digital watermark data by transforming the frequency coefficient. In addition, a method for reading digital watermark data includes the steps of calculating a probability of reading ‘1’ or ‘0’ in a read bit sequence by using a test method on the basis of binary distribution, determining the presence or absence of digital watermark data according to the probability, and reconstituting digital watermark data. Another method includes the steps of performing soft decision in code theory by assigning weights to the digital watermark sequence with a weighting function, and reconstituting digital watermark data.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a digital watermarkingtechnique. More particularly, the present invention relates to a digitalwatermarking technique for embedding or reading digital watermark datain digital data contents which represent an image or a sound. Inaddition, the present invention relates to a technique for statisticalprocessing of read watermark data in a system using the digitalwatermarking technique.

It is easy to replicate or tamper fraudulently with multimediaproduction, and the easiness hinders an data content provider fromsending data. In addition, some users may not use the data originatedfrom the provider validly. Therefore, copyright protection is stronglyneeded for the multimedia production. The digital watermarking techniqueis effective in realizing the copyright protection. According to thedigital watermarking technique, sub-data is embedded in data contentswithout being noticed by a user by utilizing redundancy of data such asof an image and a sound. The digital watermarking technique is used forprotecting a multimedia copyright by embedding copyright information, auser ID and the like as the sub-data in secret, since it is difficult toseparate the sub-data from the data contents.

2. Description of the Related Art

Conventionally, the following digital watermarking techniques areproposed.

According to a technique proposed in Japanese patent applicationNo.9-57516, “Image processing method and the apparatus,” an image issubdivided into blocks larger than a 8×8 block size which is used forcommon non reversible compression. Then, the size of the frequencycoefficient which is obtained by discrete Fourier transform of the blockis changed, the frequency coefficient being represented by a polarcoordinate system and the size being a distance from the origin point ofthe polar coordinate system. As a result, sub-data can be read correctlyeven when the non-reversible compression is performed. In addition, thefrequency coefficient is normalized within a range of predeterminedvalues, is embedded, and read. In addition, weaker image processing iscarried out on a complicated region as compared to a flat region. As aresult, degradation of image quality which may be caused by embeddingthe sub-data can be suppressed and a tolerance to contrast changing isobtained. Further, as the value of the frequency coefficient to bechanged becomes larger, the modification amount of the frequencycoefficient becomes larger (the smaller the value is, the smaller themodification amount is) so as to suppress the deterioration of imagequality more effectively. In addition, when subdividing an image intoblocks, an image area which is smaller than one block is treated as oneblock by using an average pixel value and/or using a form symmetric withrespect to a line repeatedly to compensate for the lacking image area.Moreover, the sub-data is constituted from the whole image afterweighting data of each block. As a result, the sub-data is readcorrectly even when the image is partly edited and/or the image withmany flat parts is non-reversibly compressed.

In addition, according to a technique proposed in Japanese patentapplication No.9-164466, “Information embedding method, data readingmethod and the apparatus,” when embedding data into motion pictures,data embedding is carried out to components of a relatively lowfrequency region. Further, frequency conversion is carried out with ablock size larger than a block size used for data compression, and, thendata embedding is carried out. Moreover, an original image is used whendata is read. As a result, tolerance to data compression is obtained.

Other conventional techniques are proposed in Japanese patentapplications No.8-305370, No.8-338769, No.9-9812, No.9-14388,No.9-109924, No.9-197003, No.9-218467 and No.10-33239. The digitalwatermark method is also called data hiding, finger printingsteganography, image/sound deep encryption and the like.

Elements for determining performance of the digital watermarkingtechnique are as follows:

-   -   (1) quality of data contents in which the digital watermark is        embedded;    -   (2) durability of the digital watermark which is embedded in the        data contents when the data contents are manipulated;    -   (3) safety against intentional erasing of and tampering with        digital watermark data, and    -   (4) reliability of the digital watermark data which is read from        the data contents.

The digital watermarking technique is broadly divided into two methods.One method of gives meaning to a data value by quantizing. For example,by dividing a data value by a quantization value and dividing the resultby 2, a bit data can be represented by the remainder. Another methodembeds digital watermark data by using a spread spectrum method.

The above-mentioned examples are based on the former method. In terms ofthe method, there is a problem with respect to the above element (1) inthat the digital watermark data embedded in the data contents may beperceived, or commercial value of the data contents may be lost byembedding the digital watermark data. With respect to the above element(2), the digital watermark data which is embedded in the data contentsmay be dissipated even when a general user uses the data contents in anormal way. Particularly, it is a difficult problem to achieve bothelements (1) and (2) with enough performance in practical use.

In addition, there is a method of embedding the digital watermark datarepeatedly in order to give durability to the digital watermark dataagainst manipulation of the data contents. Specifically, according tothe method, digital watermark data which is embedded repeatedly (whichis called a watermark sequence hereinafter) is read from data contents,and, then, the digital watermark data is reconstituted by performingstatistical processing. The watermark sequence has durability againstdeterioration and noise to some extent. However, if the data contentsare encoded by high compression rates, it may become difficult to readthe watermark sequence from the data contents. Therefore, it may becomeimpossible to reconstitute the digital watermark data.

In addition, as for a digital watermarking system, accuracy fordetermining the presence or absence of embedded data is important. Inaddition, reliability of embedded data is important. The digitalwatermarking system generally has a mechanism for reconstituting correctdigital watermark data even when sub-data embedded in the data contentsis corrupted to a certain extent, since the digital watermarking systemassumes various processing on the watermarked data contents. However,under present circumstances, it is impossible for the system to evaluatevalidity of reconstituted digital watermark data quantitatively.Therefore, the system does not have enough reliability.

SUMMARY OF THE INVENTION

It is a first object of the present invention to improve quality ofwatermarked digital data contents and to improve durability of digitalwatermark data against media processing of the watermarked digital datacontents.

It is a second object of the present invention to evaluatequantitatively probabilities of cases that data contents which do notcontain digital watermark data are wrongly judged as containing digitalwatermark data, and incorrect digital watermark data is read fromwatermarked digital data contents.

It is a third object of the present invention to separate a digitalwatermark data sequence, when reading watermarked digital data contents,from noise so that error bits which are included in the digitalwatermark data sequence can be reduced, thereby watermark data readingsuccess rate being improved in comparison with the conventional methodwithout changing an amount of digital watermark data and a method ofembedding the digital watermark data.

The first object of the present invention is achieved by a method forembedding digital watermark data in digital data contents. The methodincludes the steps of:

-   -   receiving the digital data contents and the digital watermark        data;    -   dividing the digital data contents into block data;    -   obtaining a frequency coefficient of the block data;    -   obtaining a complexity of the block data;    -   obtaining an amount of transformation of the frequency        coefficient from the complexity and the digital watermark data        by using a quantization width;    -   embedding the digital watermark data in said digital data        contents by transforming the frequency coefficient by the        amount; and    -   generating watermarked digital data contents.

The first object of the present invention is also achieved by a methodincluding the steps of:

-   -   receiving the digital data contents and the digital watermark        data;    -   dividing the digital data contents into block data;    -   obtaining a frequency coefficient of the block data;    -   obtaining an amount of transformation of the frequency        coefficient from the digital watermark data by using a        quantization width corresponding to the frequency coefficient,        the quantization width being obtained beforehand according to a        manipulation method of the digital data contents;    -   embedding the digital watermark data in said digital data        contents by transforming the frequency coefficient by the        amount; and    -   generating watermarked digital data contents.

According to the above-mentioned inventions, the amount oftransformation of frequency coefficients is changed and/or the amount oftransformation is increased or decreased according to the complexity ofthe digital data contents. Therefore, the quality of the watermarkeddigital data contents can be improved and the durability of digitalwatermark data against a manipulation of the watermarked digital datacontents can be improved.

The second object of the present invention is achieved by a method forreading digital watermark data embedded in digital data contents, themethod including the steps of:

-   -   receiving the digital data contents;    -   reading a bit sequence from the digital data contents;    -   calculating a probability of reading a bit ‘1’ or a bit ‘0’ in        the bit sequence by using a test method on the basis of binary        distribution;    -   determining the presence or absence of digital watermark data        according to the probability; and    -   reconstituting and generating the digital watermark data from        the bit sequence.

According to the above-mentioned invention, probabilities of thefollowing cases can be evaluated quantitatively. The cases are thatdigital data contents which do not contain digital watermark data arewrongly judged as containing digital watermark data, and incorrectdigital watermark data is read from watermarked digital data contents.In addition, the probability can be suppressed within a constant value.

The third object of the present invention is achieved by a method forreading digital watermark data from digital data contents in which eachbit of digital watermark data is embedded a plurality of times, themethod including the steps of:

-   -   receiving digital data contents;    -   reading a digital watermark sequence from the digital data        contents;    -   performing soft decision in code theory by assigning weights to        the digital watermark sequence with a weighting function;    -   reconstituting the digital watermark data from the digital        watermark sequence.

According to the above-mentioned invention, the digital watermark datasequence is separated from the noise so that error bits which areincluded in the digital watermark data sequence can be reduced, therebythe digital watermark data reading success rate being improved incomparison with the conventional method. In addition, since weights areassigned to the digital watermark data sequence, the present inventionis especially effective when the repeating number of watermark embeddingis small.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention willbecome more apparent from the following detailed description when readin conjunction with the accompanying drawings, in which:

FIG. 1 is a block diagram of a digital watermarking system of thepresent invention;

FIG. 2 is a general flowchart showing a digital watermark embeddingprocess according to a conventional technique;

FIG. 3 is a detailed flowchart showing a principal part of the digitalwatermark embedding process according to the conventional technique;

FIG. 4 is a conceptual diagram of the digital watermark embeddingprocess according to the conventional technique;

FIG. 5 is a general flowchart showing a digital watermark readingprocess according to the conventional technique;

FIG. 6 is a detailed flowchart showing a principal part of the digitalwatermark reading process according to the conventional technique;

FIG. 7 is a block diagram showing receiving data and generating data ofa digital watermark embedding apparatus of the present invention;

FIG. 8 is a block diagram showing receiving data and generating data ofa digital watermark reading apparatus of the present invention;

FIG. 9 is a general flowchart showing a digital watermark embeddingprocess according to a first embodiment of the present invention;

FIG. 10 is a detailed flowchart showing a principal part of the digitalwatermark embedding process according to the first embodiment of thepresent invention;

FIGS. 11A and 11B are conceptual diagrams of the digital watermarkembedding process according to the first embodiment of the presentinvention;

FIG. 12 is a flowchart of a process for calculating a data complexityaccording to a second embodiment of the present invention;

FIG. 13 is a flowchart showing a process for obtaining a watermarkweight ratio data according to the present invention;

FIG. 14 is a detailed flowchart showing a principal part of the digitalwatermark embedding process according to a third embodiment of thepresent invention;

FIG. 15 is a detailed flowchart showing a principal part of the digitalwatermark reading process according to a fourth embodiment of thepresent invention;

FIG. 16 is a flowchart showing a process of calculating a watermarkstrength matrix according to a fifth embodiment of the presentinvention;

FIG. 17 is a block diagram of a computer;

FIG. 18 is a block diagram of an integrated circuit;

FIG. 19 is a block diagram of a digital watermarking system of thepresent invention;

FIG. 20 is a block diagram of a digital watermark reading apparatusshown in FIG. 19;

FIG. 21 is a diagram for explaining judgment on digital watermark data;

FIG. 22 is a conceptual diagram of reconstituting digital watermarkdata;

FIG. 23 is a flowchart of a digital watermark reading process accordingto a seventh embodiment of the present invention;

FIG. 24 is a block diagram of a digital watermarking system according toan eighth embodiment of the present invention;

FIG. 25 is a flowchart of a digital watermark reading process accordingto a tenth embodiment of the present invention;

FIG. 26 is a flowchart of a digital watermark reading process accordingto a tenth embodiment of the present invention when reading digitalwatermark data sequence which is embedded after being modulated by apseudo-random sequence;

FIG. 27 is a diagram showing the result of reading a digital watermarkdata sequence without modulation;

FIG. 28 is a diagram showing the result of reading a modulated digitalwatermark data sequence;

FIG. 29 is a diagram showing a digital watermark reading processaccording to a conventional technique;

FIG. 30 is a graph showing how MPEG-1 coding changes ‘1’ data bit,specifically the graph shows occurrence frequency with respect to changeamount of a DCT coefficient value by 1.5-Mbps MPEG-1 coding;

FIG. 31 is a flowchart showing a principle of a thirteenth embodiment ofthe present invention corresponding to a third object;

FIG. 32 is a block diagram of a digital watermark reading apparatusaccording to the thirteenth embodiment of the present invention;

FIG. 33 is a general flowchart showing a digital watermark readingprocess according to the thirteenth embodiment of the present invention;

FIG. 34 is a diagram showing the result of comparison of a digitalwatermark data reading success rate between a conventional readingmethod and the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Before explaining embodiments of the present invention, definition ofsome words will be given. “Digital watermark data sequence”represents adata sequence read from the digital data contents before beingreconstituted. “Digital watermark data” represents significant data forsystem operation, which data needs to be embedded in the digital datacontents, or, data obtained by reconstituting the digital watermarksequence. “Reliability α of digital watermark” is an index representingvalidity. of read digital watermark data. That is, it represents aprobability that the read digital watermark data matches with the actualembedded digital watermark data. Conversely, a probability of readingdigital watermark data from an image without digital watermark data orreading erroneous digital watermark data can be represented as 2(1−α).Similarly, “embedded sequence” represents data to be actually embedded.The embedded sequence includes sequence of embedded data which ismodulated, extended or repeated. In addition, “read” may be replacedwith “extract” in some cases.

FIG. 1 shows a digital watermarking system of the present invention. Inthe system shown in FIG. 1, digital watermark data 101 is embedded indigital data contents 103 by a digital watermark embedding apparatus102, then, converted into watermarked digital data contents 104.

The watermarked digital data contents 104 are degraded to watermarkeddigital data contents 105 by compression or image processing while thewatermarked digital data contents 104 are distributed by wireless orwire communication or by a packaged medium.

A digital watermark reading apparatus 106 reads a watermark sequencefrom the degraded watermarked digital data contents 105, andreconstitutes digital watermark data 107.

In the following, a digital watermark embedding method and a digitalwatermark reading method by using quantization will be described, sinceembodiments of the present invention are based on the methods. After thedescription of the methods, the embodiments of the present inventionwill be described.

According to the digital watermarking technique based on quantization,digital watermark data is embedded by quantizing all or a part of datawhich is transformed (for example, by an orthogonal transform) fromoriginal digital data contents, or not-yet-transformed data. As fordigital watermark data reading, data in the contents in which digitalwatermark data is embedded is quantized by the same value as a valueused for embedding digital watermark data, and, then digital watermarkdata is determined from the quantized data value.

In the following, a general outline of the methods will be described.The Japanese patent application No. 9-57516, “Image processing methodand the apparatus”, and the Japanese patent application No. 9-164466,“Information embedding method, data reading method and the apparatus”,and the like can be referred to for obtaining detailed information ofthe digital watermarking technique based on quantization.

First, digital watermark embedding method based on quantization will bedescribed. A process of the method is carried out by the digitalwatermark embedding apparatus 102 shown in FIG. 1. FIG. 2 is a flowchartshowing the process.

The digital watermark embedding apparatus 102 obtains block data 109 bydividing digital data contents 103 into a plurality of blocks (m blocksin this example) in step 100. Then, a frequency coefficient matrix 115(an orthogonal transform coefficient matrix) is generated by performingan orthogonal transform on the block data 108 in step 110.

A pseudo-random sequence 125 is generated from input key data 12 in step120. Then, a coefficient (for each block) from the coefficient matrix115 is selected one by one using the pseudo-random sequence 125 so as togenerate a frequency coefficient sequence 135 to be watermarked in step130. Each bit of the digital watermark data 101 are diffused byrepeating number (t) of embedding so that a digital watermark sequence145 is generated in step 140. The digital watermark sequence 145 isembedded into the frequency coefficient sequence 135 such that awatermarked frequency coefficient sequence 155 is generated in step 150.

After that, the frequency coefficient sequence 135 in the frequencycoefficient matrix 115 is replaced by the watermarked frequencycoefficient sequence 155 to generate a watermarked frequency coefficientmatrix 165 in step 160. Then, the watermarked frequency coefficientmatrix 165 is inverse-orthogonal-transformed to form a watermarked blockdata 175 in step 170. After that, the block data part of the inputdigital data contents 103 is replaced by the watermarked block data 175in step 180. As a result, a watermarked digital data contents is output.

In the above description, data in which digital watermark data isembedded is assumed to be the coefficient of the frequency coefficientmatrix. However, the data can be a pixel. In addition, when selecting acoefficient value from a block image, the number of the selectedcoefficient is not limited to one, that is, it can be more than one orzero. The present invention does not depend on the matter.

In the process of diffusing the digital watermark data shown in FIG. 2,for example, a process represented by s[j][k]=w[j] is carried out forall j and k, then, the digital watermark data (w[0],w[1], . . . ,w[n-1])is transformed to the digital watermark data sequence s[0][0],s[0][1], .. . ,s[0][t-1],s[1][0],s[1][1], . . . ,s[1][t-1],s[n-1][0],s[n-1][1], .. . ,s[n-1][t-1].

In the watermark embedding process, quantization widths of frequencycoefficients q[0],q[1], . . . ,q[m-1] are used.

In the following, the watermark embedding process (step 150) will bedescribed in detail with reference to a flowchart shown in FIG. 3.

Let the repeating number t of each bit of the digital watermark data be${t = \lfloor \frac{m}{n} \rfloor},$the frequency sequence be w[j],s[j][k] ε {0,1} {0≦j<n,0≦k<t}.

The watermark embedding process to the frequency sequence {f[i]} iscarried out as follows.

1. Following steps are carried out for all${i( {0 \leq i < {\lfloor \frac{m}{n} \rfloor \cdot n}} )}.$

2. A watermarked frequency coefficient f′[i] is obtained from thefrequency coefficient f[i] according to following steps.$ {{ {{ i )\quad{If}\quad\lfloor {\frac{f\lbrack i\rbrack}{q} + \frac{1}{2}} \rfloor\quad{mod}\quad 2\quad{is}\quad{equal}\quad{to}\quad{{s\lbrack X\rbrack}\lbrack Y\rbrack}},\quad {f^{\prime}\lbrack i\rbrack}arrow{\lfloor {\frac{f\lbrack i\rbrack}{q} + \frac{1}{2}} \rfloor \times {q.{ii}}} } )\quad{If}\quad\lfloor {\frac{f\lbrack i\rbrack}{q} + \frac{1}{2}} \rfloor\quad{mod}\quad 2\quad{is}\quad{different}\quad{from}}\quad\quad{{{{s\lbrack X\rbrack}\lbrack Y\rbrack}\quad{and}\quad\lfloor {\frac{f\lbrack i\rbrack}{q} + \frac{1}{2}} \rfloor\quad{is}\quad{equal}\quad{to}\quad\lfloor \frac{f\lbrack i\rbrack}{q} \rfloor},\quad {f^{\prime}\lbrack i\rbrack}arrow{( {\lfloor {\frac{f\lbrack i\rbrack}{q} + \frac{1}{2}} \rfloor + 1} ) \times {q.{iii}}} }} )\quad{If}\quad\lfloor {\frac{f\lbrack i\rbrack}{q} + \frac{1}{2}} \rfloor{mod}\quad 2\quad{is}\quad{different}\quad{from}$$\quad{{{{s\lbrack X\rbrack}\lbrack Y\rbrack}\quad{and}\quad\lfloor {\frac{f\lbrack i\rbrack}{q} + \frac{1}{2}} \rfloor\quad{is}\quad{different}\quad{from}\quad\lfloor \frac{f\lbrack i\rbrack}{q} \rfloor},\quad {f^{\prime}\lbrack i\rbrack}arrow{( {\lfloor {\frac{f\lbrack i\rbrack}{q} + \frac{1}{2}} \rfloor - 1} ) \times {q.}} }$Here, X=i/t and Y=i mod t. In addition, └x┘ represents a maximum numberwhich does not exceed x and x mod y represents the remainder of xdivided by y.

FIG. 4 shows the concept of the conventional watermark embeddingprocess. As shown in the figure, digital watermark data is embedded bychanging a data value of watermarking area to a central value of thequantization width.

Next, the digital watermark reading method based on quantization will bedescribed. The process is carried out in the digital watermark readingapparatus 106. According to the digital watermark reading process, adigital watermark data sequence is read from watermarked contents, and,then digital watermark data is reconstituted by statistically processingthe digital watermark data sequence.

FIG. 5 is a flowchart showing the conventional digital watermark readingprocess based on quantization.

The digital watermark reading apparatus 106 obtains watermarked blockdata 205 by dividing watermarked digital data contents 105 into aplurality of blocks (m blocks in this example) in step 200. Then, afrequency coefficient matrix 215 is generated by performing anorthogonal transform on the watermarked block data 205 in step 210.

A pseudo-random sequence 225 is generated from input key data 22 in step220. Then, a coefficient value (for each block) of the frequencycoefficient matrix 215 is selected one by one using the pseudo-randomsequence 225 so as to generate a watermarked frequency coefficientsequence 235 in step 230. Then, the watermark reading process isperformed on the watermarked frequency sequence 235 so that a digitalwatermark sequence 245 is read in step 240. Finally, the originalwatermark data 107 is output by performing statistical processing on thedigital watermark data sequence in step 250.

Next, the digital watermark reading process (step 240) will be describedin detail with reference to a flowchart in FIG. 6. The process forreading the digital watermark sequence from the watermarked frequencycoefficient sequence {f′[i]} is shown in the following.

1. Following steps are carried out for all$i( {0 \leq i < {\lfloor \frac{m}{n} \rfloor \cdot n}} )$by using a frequency coefficient quantization width q.

2. The digital watermark sequence s[X][Y] is read from the frequencycoefficient f′[i]. That is,${{s\lbrack X\rbrack}\lbrack Y\rbrack} = {\lfloor {\frac{f^{\prime}\lbrack i\rbrack}{q} + \frac{1}{2}} \rfloor{mod}\quad 2.}$${Here},{X = {{\lfloor \frac{i}{t} \rfloor\quad Y} = {i\quad{mod}\quad{t.}}}}$

When the digital watermark data is reconstituted from the digitalwatermark data sequence by performing statistical processing, a majoritydecision method such as ${W\lbrack j\rbrack} = \{ {\begin{matrix}1 & {{\sum\limits_{k = 0}^{t - 1}{{s\lbrack j\rbrack}\lbrack k\rbrack}} \geq \frac{t}{2}} \\0 & {{\sum\limits_{k = 0}^{t - 1}{{s\lbrack j\rbrack}\lbrack k\rbrack}} < \frac{t}{2}}\end{matrix}( {0 \leqq j < n} )} $is used.

Next, the present invention corresponding to the first object will bedescribed.

FIG. 7 is a block diagram showing input data and output data of thedigital watermark embedding apparatus of the present invention. Thedigital watermark embedding apparatus 102 inputs digital data contents103 such as an image and a sound as main data, key data 12 and digitalwatermark data 101 as sub-data. The digital watermark embeddingapparatus 102 embeds digital watermark data 101 into the digital datacontents 103 and outputs watermarked digital data contents 104.

FIG. 8 is a block diagram showing input data and output data of thedigital watermark reading apparatus of the present invention. Thedigital watermark reading apparatus 20 inputs the watermarked digitaldata contents 21 and the key data 22, and outputs digital watermark data23 embedded in the watermarked digital data contents 21. Here, the keydata 22 is the same as the key data 12.

In the following, embodiments of the present invention will bedescribed.

First Embodiment

A first embodiment of the present invention will be described. Accordingto the first embodiment, digital data contents and digital watermarkdata is received and the digital data contents are divided into blockdata. Then, a frequency coefficient of the block data and the complexityis obtained. Next, an amount of transformation of the frequencycoefficient is obtained from the complexity and the digital watermarkdata by using a quantization width, and the digital watermark data isembedded by transforming the frequency coefficient by the amount. Then,watermarked digital data contents is generated.

The process of the first embodiment is a modified process of the digitalwatermark embedding process shown in FIG. 2, in which the modified partis the main part for watermark embedding.

FIG. 9 is a flowchart of the whole process of the first embodiment. InFIG. 9, a step 190 which calculates the complexity and a watermarkembedding process for varying the transformation amount according to thecomplexity (steps 195, 150) are different from the conventional processshown in FIG. 2. Therefore, the different point will be mainly describedin the following.

Block data 108 is input, and a complexity sequence 195 is generated bycalculating a data complexity e[i](0≦e[i]≦1) for each block data in step190. Then, the coefficient value of data to be watermarked istransformed to a value within quantization width according to the datacomplexity. In this embodiment, it is possible to use a conventionalmethod for calculating the data complexity. For example, in the case ofan image, a process for obtaining local image complexity can be used. Inthis case, it is necessary to normalize the range of the localcomplexity such that the range becomes from 0 to 1, if the range is from−αto +β.

Next, the watermark embedding process which is the heart of the secondembodiment will be described in detail. FIG. 10 is a flowchart showingthe watermark embedding process (step 150 in FIG. 9) in detail.

The process for embedding digital watermark data into a frequencycoefficient sequence {f[i]} of the first embodiment is carried out asfollows.

1. For all${i( {0 \leq i < {\lfloor \frac{m}{n} \rfloor \cdot n}} )},$the following process is carried out.

2. A watermarked coefficient f′[i] is obtained from a coefficient f[i].$ {{ {{ i )\quad{If}\quad\lfloor {\frac{f\lbrack i\rbrack}{q} + \frac{1}{2}} \rfloor\quad{mod}\quad 2\quad{is}\quad{equal}\quad{to}\quad{{s\lbrack X\rbrack}\lbrack Y\rbrack}},\quad {f^{\prime}\lbrack i\rbrack}arrow{{f\lbrack i\rbrack} + {( {{\lfloor {\frac{f\lbrack i\rbrack}{q} + \frac{1}{2}} \rfloor \times q} - {f\lbrack i\rbrack}} ) \times {{e\lbrack i\rbrack}.{ii}}}} } )\quad{If}\quad\lfloor {\frac{f\lbrack i\rbrack}{q} + \frac{1}{2}} \rfloor\quad{mod}\quad 2\quad{is}\quad{not}\quad{equal}\quad{to}}\text{}\quad{{{{s\lbrack X\rbrack}\lbrack Y\rbrack}\quad{and}\quad\lfloor {\frac{f\lbrack i\rbrack}{q} + \frac{1}{2}} \rfloor\quad{is}\quad{equal}\quad{to}\quad\lfloor \frac{f\lbrack i\rbrack}{q} \rfloor},\quad {f^{\prime}\lbrack i\rbrack}arrow{( {\lfloor {\frac{f\lbrack i\rbrack}{q} + \frac{1}{2}} \rfloor + \frac{{e\lbrack i\rbrack} + 1}{2}} ) \times q} }{iii}} )\quad{If}\quad\lfloor {\frac{f\lbrack i\rbrack}{q} + \frac{1}{2}} \rfloor{mod}\quad 2\quad{is}\quad{not}\quad{equal}\quad{to}$$\quad{{{{s\lbrack X\rbrack}\lbrack Y\rbrack}\quad{and}\quad\lfloor {\frac{f\lbrack i\rbrack}{q} + \frac{1}{2}} \rfloor\quad{is}\quad{not}\quad{equal}\quad{to}\quad\lfloor \frac{f\lbrack i\rbrack}{q} \rfloor},\quad {f^{\prime}\lbrack i\rbrack}arrow{( {\lfloor {\frac{f\lbrack i\rbrack}{q} + \frac{1}{2}} \rfloor - \frac{{e\lbrack i\rbrack} + 1}{2}} ) \times {q.}} }$Here, q represents the quantization width for digital watermark dataembedding, X=i/j, Y=imodt, and └x┘ is the maximum integer which does notexceed x, and x mod y represents the remainder of x divided by y.

FIGS. 11A and 11B are conceptual diagrams showing the digital watermarkembedding process of the first embodiment. As shown in FIG. 11B, a datacomplexity e[i](0≦e[i]≦1) is calculated for each block data, then, thevalue of data in which digital watermark data is embedded is transformedto a value within the quantization width according to the datacomplexity.

Generally, the quality of the watermarked digital data contents is atrade-off for the strength of the digital watermark data. However,according to the present invention, both of the quality of thewatermarked digital data contents and the watermark durability can beimproved while keeping the quality and the durability in balance. Thatis, digital watermark data is embedded according to the local datacomplexity. Specifically, digital watermark data is embedded with agreater strength in a complex part, and is embedded with a weakerstrength in a non-complex part.

The watermarking technique has an embedding process and a readingprocess in a pair. However, even if the embedding process is modifiedfrom the conventional process according to the present invention, thereading process does not need to be changed from the conventionalreading process for reading the digital watermark data which is embeddedby the method of the present invention.

Second Embodiment

In the following, a second embodiment of the present invention will bedescribed. The second embodiment relates to the process for calculatingthe data complexity (step 190 in FIG. 9).

According to the second embodiment, the block data is transformed byapplying Wavelet transform. Then, high frequency coefficient data of thewavelet transformed data is filtered by using a threshold value, and thecomplexity of the block data is calculated from the number of the datavalues which exceed the threshold.

FIG. 12 is a flowchart of the process for calculating the datacomplexity according to the second embodiment. Here, let the dimensionof a block data B[i] be N, and let the size of the block data be M₀×M₁ .. . ×M_(N-1). A following process is performed on each elementh_(v0,v1, . . . ,vN-1)(0<v_(u)<M_(u)/2, 0<u<N) of the high frequencycoefficient matrix H₀×H₁ . . . ×H_(N-1) of N dimensional wavelettransformed block data.

1. count←0

2. For all (v₀,v₁, . . . ,v_(N-1)) , a step 3 is carried out (Ndimensional loop).

3. For a threshold Δ≧0 which is set beforehand, If |hv₀,v₁, . . .,v_(N-1)|≧Δ, count←count+1. Here, |X| represents the absolute value ofx.

4. For a threshold Γ≧0 which is set beforehand, If count≧Γ, e[i]←1.0 Ifnot,$ {e\lbrack i\rbrack}arrow{\frac{count}{\Gamma}.} $

In the process for calculating the data complexity, for example, if itis assumed that N=2 (an image), the basis of the wavelet transform isthe Haar basis, M₀=16 and M₁=16, an experiment shows that values of Δ=4and Γ=16 are good for the balance for embedding digital watermark datawithout being notified by a human.

According to the second embodiment, the above-mentioned function can berealized by setting the two thresholds Δ and Γ according to thecharacteristics of the watermarking technique such as the kind of datato be watermarked, a unit (the size of the block data), the kind oforthogonal transform to be used. By applying the above-mentionedfunction to the watermarking technique, it becomes possible to embeddigital watermark data more appropriately according to characteristicsof individual digital data contents.

Third Embodiment

In the following, a fourth embodiment of the present invention will bedescribed.

According to the third embodiment, in the digital watermark embeddingprocess, block data of digital data contents is obtained, and atransformation amount of frequency coefficient is calculated on thebasis of a transformation amount for each frequency band according to amanipulation method of the digital data contents. Then, block data ofthe watermarked digital data contents is generated.

Let the dimension of a block data B[i] be N and the size be M₀×M₁ . . .×M_(N-1). Here, a sequence which represents the ratio of transformationwidth for the frequency band of each frequency coefficient needs to beobtained beforehand by using adequate digital data contents beforeoperating a digital watermarking system. The calculation method forobtaining q[i] will be described in detail in a fifth embodiment later.

FIG. 13 is a flowchart for obtaining the ratio of the quantization withfor each frequency band. First, digital data contents 1000 is input, andblock data 1015 is obtained by dividing the input digital data contentsinto blocks in step 1010. The block data 1015 is transformed to firstfrequency coefficient matrices by applying the orthogonal transform instep 1020. Next, digital data contents 1035 is generated by performing amanipulation such as non-reversible compression on the digital datacontents 1000 in step 1030. Then, block data 1045 is generated bydividing the digital data contents 1035 into blocks in step 1040. Secondfrequency matrices 1055 is generated by applying the orthogonaltransform to the block data 1015 in step 1055. Then, the variance of thedistribution of the difference between each element of the frequencycoefficients matrices 1025 and each element of the frequencycoefficients matrices 1055 is obtained in step 1060. Finally, watermarkweight ratio data d v₀,v₁, . . . ,v_(N-1) 1070 which represents theratio of transformation for each frequency coefficient is obtained. Thewatermark weight ratio data obtained in this way is stored, and it isused in a watermark embedding process and a watermark reading process asnecessary. The quantization width is obtained as dv₀,v₁, . . .,v_(N-1)×Power which will be described next.

FIG. 14 is a flowchart showing the watermark embedding process which isthe heart of the third embodiment of the present invention. Here, theflow of the whole process is the same as that shown in FIG. 2 or FIG. 9.

Let the watermark weight ratio sequence be {dv₀,v₁, . . . ,v_(N-1)}(0≦v_(u)<M_(u), 0≦u<N), and let the watermark strength be Power (thewatermark strength represents durability of digital watermark dataagainst manipulations of watermarked digital data contents.)

The watermark embedding process of the embodiment is carried out asfollows.

1. For all${i( {0 \leq i < {\lfloor \frac{m}{n} \rfloor \cdot n}} )},$a following process is carried out.

2. A quantization width q[i] used when embedding digital watermark datainto the frequency coefficient f[i] is obtained by q[i]←dv₀,v₁, . . .,v_(N-1)×Power by using an element dv₀,v₁, . . . ,v_(N-1) of thewatermark weight ratio sequence which corresponds to the band of thefrequency coefficient f[i] (f[i] is a (v₀,v₁, . . . ,v_(N-1))thcomponent of the frequency coefficient matrices).

3. The watermarked frequency coefficient f′[i] is obtained from thefrequency coefficient f[i] in the following way.${ i )\quad{If}\quad\lfloor {\frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} + \frac{1}{2}} \rfloor\quad{mod}{\quad\quad}2\quad{is}\quad{equal}\quad{to}\quad{{s\lbrack X\rbrack}\lbrack Y\rbrack}},\quad {f^{\prime}\lbrack i\rbrack}arrow{\lfloor {\frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} + \frac{1}{2}} \rfloor \times {{q\lbrack i\rbrack}.{ii}}\text{)}\quad{If}\quad\lfloor {\frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} + \frac{1}{2}} \rfloor\quad{mod}\quad 2\quad{is}\quad{not}\quad{equal}\quad{to}\quad{{s\lbrack X\rbrack}\lbrack Y\rbrack}\quad{and}} $$\quad{{\lfloor {\frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} + \frac{1}{2}} \rfloor\quad{is}\quad{equal}\quad{to}\quad\lfloor \frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} \rfloor},\quad {f^{\prime}\lbrack i\rbrack}arrow{( {\lfloor {\frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} + \frac{1}{2}} \rfloor + 1} ) \times {q\lbrack i\rbrack}} }$${iii}\text{)}\quad{If}\quad\lfloor {\frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} + \frac{1}{2}} \rfloor\quad{mod}{\quad\quad}2\quad{is}\quad{not}\quad{equal}\quad{to}\quad{{s\lbrack X\rbrack}\lbrack Y\rbrack}\quad{and}$$\quad{{\lfloor {\frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} + \frac{1}{2}} \rfloor\quad{is}\quad{not}\quad{equal}\quad{to}\quad\lfloor \frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} \rfloor},\quad {f^{\prime}\lbrack i\rbrack}arrow{( {\lfloor {\frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} + \frac{1}{2}} \rfloor - 1} ) \times {{q\lbrack i\rbrack}.}} }$Here, X=i/t, Y=i mod t, and └x┘ is the maximum integer which does notexceed x, and x mod y represents the remainder of x divided by y.

Fourth Embodiment

In the following, a fourth embodiment of the present invention will bedescribed.

The fourth embodiment is a watermark reading process corresponding tothe watermark embedding process of the third embodiment. According tothe fourth embodiment, block data of watermarked digital data contentsis obtained, and digital watermark data is read from frequencycoefficients on the basis of transformation amount for each frequencyband according to a manipulation method of the digital data contents.

FIG. 15 is a flowchart showing the watermark reading process of thefourth embodiment of the present invention. Here, as in the case of thethird embodiment, let the watermark weight ratio sequence be {dv₀,v₁, .. . ,v_(N-1)} (0≦v_(u)<M_(u), 023 u<N), and let the watermark strengthbe Power (the watermark strength represents durability of digitalwatermark data against manipulations such as non-reversible compressionto watermarked digital data contents.)

The process for reading the digital watermark data sequence from thewatermarked frequency coefficient according to the fourth embodiment iscarried out as follows.

1. For all${i\quad( {0 \leq i < {\lfloor \frac{m}{n} \rfloor \cdot n}} )},$a following process is carried out.

2. A quantization width q[i] used when reading digital watermark datafrom the frequency coefficient f′[i] is obtained by q[i]←dv₀,v₁, . . .,v_(N-1)×Power by using an element dv₀,v₁, . . . ,v_(N-1) of thewatermark weight ratio sequence which corresponds to the band offrequency coefficient f[i] (f[i] is a (v₀,v₁, . . . ,v_(N-1))thcomponent of the frequency coefficient matrices).

3. The digital watermark data sequence s[X][Y] is read from thewatermarked frequency coefficient f′[i] in the following way.$ {{s\lbrack X\rbrack}\lbrack Y\rbrack}arrow{\lfloor {\frac{f^{\prime}\lbrack i\rbrack}{q\lbrack i\rbrack} + \frac{1}{2}} \rfloor\quad{mod}{\quad\quad}2} $${Here},{X = {{\lfloor \frac{i}{t} \rfloor\quad{and}\quad Y} = {i\quad{mod}{\quad\quad}{t.}}}}$

According to the above-mentioned third and fourth embodiment, thewatermark embedding strength can be changed according to the frequencyband. Specifically, the watermark embedding and reading methodapplicable for a manipulation method becomes possible. In the method,according to the amount of change of digital data contents from originaldata for each frequency band due to manipulation such as non-reversiblecompression, the watermark strength is raised to a band when the amountis large, and the watermark strength is reduced when the amount issmall. Accordingly, both of the quality of watermarked digital datacontents and the durability of digital watermark data can be improved ata time.

Fifth Embodiment

In the following, a fifth embodiment of the present invention will bedescribed. According to the fifth embodiment, a number of digital datacontents (images, sounds and the like) are prepared and calculation of awatermark strength matrix is carried out for each frequency band.

A processing flow of the fifth embodiment is the same as that shown inFIG. 13 basically. Here, the orthogonal transform process shown in FIG.13 is the same as an orthogonal transform process used for digitalwatermarking process. For example, if the orthogonal transform used fordigital watermarking is discrete cosine transformation (DCT) for a 16×16size, the DCT is used, and, if the transformation used for digitalwatermarking is fast Fourier transform (FFT) for an 128×128 size, theFFT is used.

FIG. 16 is a flowchart showing the process of calculating the watermarkstrength matrix for each frequency band according to the fifthembodiment.

Here, let the frequency coefficient matrices be N, the size be M₀×M₁ . .. ×M_(N-1), and each of the components be x0 _(v0,v1, . . . ,vN-1),xt_(v0,v1, . . . ,v) _(N-1)(0≦v_(u)<M_(u), 0≦u<N). The process shown inFIG. 16 is as follows.

1. For all i (0≦i<m), the following steps 2 and 3 are performed.

2. For all (ν₀,ν₁, . . . ,ν_(N-1))=(0,0, . . . ,0)˜(M₀,M₁, . . .,M_(N-1)), the process of the following step 3 is performed.3.  y_(v₀, v₁, …  , v_(N − 1))^((i)) ← x  o_(v₀, v₁, …  , v_(N − 1)) − x  t_(v₀, v₁, …  , v_(N − 1))

4. For all (ν₀,ν₁, . . . ,ν_(N-1))=(0,0, . . . ,0)˜(M₀,M₁, . . .,M_(N-1)), the following steps 5 and 6 are performed.$ {5.\quad A_{v_{0},v_{1},\ldots\quad,v_{N - 1}}}arrow\frac{\sum\limits_{i = 0}^{m - 1}y_{v_{0},v_{1},\ldots\quad,v_{N - 1}}^{(i)}}{m} $$ {6.\quad d_{v_{0},v_{1},\ldots\quad,v_{N - 1}}}arrow\sqrt{\frac{\sum\limits_{i = 0}^{m - 1}( {y_{v_{0},v_{1},\ldots\quad,v_{N - 1}}^{(i)} - A_{v_{0},v_{1},\ldots\quad,v_{N - 1}}} )^{2}}{m}} $

According to the fifth embodiment, it becomes possible to set thewatermark strength to a level that is suitable for each frequency bandaccording to a manipulation method for digital data contents such asnon-reversible compression. For example, if the watermark strength isPower and the distribution of the amount of change of each coefficientvalue of the frequency coefficients after a manipulation can beapproximated by a Laplacian distribution, when digital watermark data isread from digital data contents on which an assumed manipulation isperformed, the rate of bit reversal for the extracted digital watermarkdata can be made constant ${\mathbb{e}}^{- \frac{Power}{\sqrt{2}}}$regardless of the frequency band (e is the natural logarithm). It is theadvantage of the present invention to be able to predict the rate of bitreversal with the constant formula. In addition, according to theembodiment of the present invention, one of the problem of theconventional method that durability of embedded digital watermark datais varied according to the position of the frequency coefficient issolved. That is, the durability of the embedded digital watermark datais constant regardless of the position of the frequency coefficient(which is obvious from the above formula). The embodiment can be appliednot only to the watermarking method based on quantization but also to awatermarking method based on the spread spectrum technique.

Sixth Embodiment

In the following, a sixth embodiment of the present invention will bedescribed. According to the sixth embodiment, the digital watermarkembedding process is carried out by utilizing the first embodiment andthe third embodiment in combination. The watermark embedding process ofthe sixth embodiment will be described as a modification of the step 150shown in FIG. 9.

According to the sixth embodiment, the process for embedding digitalwatermark data in a frequency coefficient sequence {f[i]} is as follows.

1. For all${i\quad( {0 \leq i < {\lfloor \frac{m}{n} \rfloor \cdot n}} )},$the following is performed.

2. A quantization width q[i] used when embedding digital watermark datainto the frequency coefficient f[i] is obtained by q[i]←dv₀,v₁, . . .,v_(N-1)×Power by using an element dv₀,v₁, . . . ,v_(N-1) of thewatermark weight ratio sequence which corresponds to the band ofthe,frequency coefficient f[i].

3. The watermarked coefficient f′[i] is obtained from the frequencycoefficient f[i] in the following way.${ i )\quad{If}\quad\lfloor {\frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} + \frac{1}{2}} \rfloor\quad{mod}{\quad\quad}2\quad{is}\quad{equal}\quad{to}\quad{{s\lbrack X\rbrack}\lbrack Y\rbrack}},\quad {f^{\prime}\lbrack i\rbrack}arrow{{f\lbrack i\rbrack} + {( {{\lfloor {\frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} + \frac{1}{2}} \rfloor \times {q\lbrack i\rbrack}} - {f\lbrack i\rbrack}} ) \times {{e\lbrack i\rbrack}.{ii}}\text{)}\quad{If}\quad\lfloor {\frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} + \frac{1}{2}} \rfloor\quad{mod}{\quad\quad}2\quad{is}\quad{not}\quad{equal}\quad{to}\quad{{s\lbrack X\rbrack}\lbrack Y\rbrack}\quad{and}}} $$\quad{{\lfloor {\frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} + \frac{1}{2}} \rfloor\quad{is}\quad{equal}\quad{to}\quad\lfloor \frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} \rfloor},\quad {f^{\prime}\lbrack i\rbrack}arrow{( {\lfloor {\frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} + \frac{1}{2}} \rfloor + \frac{{e\lbrack i\rbrack} + 1}{2}} ) \times {{q\lbrack i\rbrack}.{iii}}\text{)}\quad{If}\quad\lfloor {\frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} + \frac{1}{2}} \rfloor\quad{mod}\quad 2\quad{is}\quad{not}\quad{equal}\quad{to}\quad{{s\lbrack X\rbrack}\lbrack Y\rbrack}\quad{and}} }$$\quad {\lfloor {\frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} + \frac{1}{2}} \rfloor\quad{is}\quad{not}\quad{equal}\quad{to}\quad{\lfloor \frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} \rfloor.\quad{f^{\prime}\lbrack i\rbrack}}}arrow{( {\lfloor {\frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} + \frac{1}{2}} \rfloor - \frac{{e\lbrack i\rbrack} + 1}{2}} ) \times {{q\lbrack i\rbrack}.}} $Here, X=i/t, Y=i mod t, and └x┘ is the maximum integer which does notexceed x, and x mod y represents the remainder of x divided by y.

According to the sixth embodiment, both of the quality of thewatermarked digital data contents and the durability of digitalwatermark data can be further improved as compared with the firstembodiment and the third embodiment applied separately. The watermarkreading method shown in the fourth embodiment can be used as-is for awatermark reading method in the sixth embodiment.

The above-mentioned processes performed by the digital watermark readingapparatus and the digital watermark embedding apparatus according to thepresent invention can be constructed by a program which can be stored ina computer readable medium such as a disk unit, a floppy disk, CD-ROMand the like. Then, by installing the program into a computer from themedium, the present invention can be easily realized. FIG. 17 is adiagram showing the configuration example of the computer. As shown inthe figure, the computer includes a CPU300, a memory 301, an externalstorage unit 302, a display 303, a keyboard 304 and a communicationprocessing unit 305. The digital watermarking process of the presentinvention is carried out by running the program stored in the memory 301on the CPU 300.

In addition, the digital watermark reading apparatus and the digitalwatermark embedding apparatus can be realized also by an integratedcircuit shown in FIG. 18. The integrated circuit includes a memory part401, a micro processor part 402, an interface part 403 managing aninterface to an outside part. Since, the configuration in FIG. 18 showsprincipal parts, the integrated circuit may includes other parts. Theprogram stored in the memory part 401 is carried out by a microprocessor part 402. The integrated circuit can take various otherconfigurations. The integrated circuit can be incorporated to variousapparatuses such as a camera so that the apparatuses can perform thedigital watermarking process of the present invention.

As mentioned above, according to the present invention, the rate of theamount of change of frequency coefficients is changed, and/or, theamount of change of rate is increased or decreased according to thecomplexity of the digital data contents. Therefore, the quality of thewatermarked digital data contents can be improved and the durability ofdigital watermark data against a manipulation of the watermarked digitaldata contents can be improved.

Next, embodiments of the present invention corresponding to the secondobjectives will be described.

Seventh Embodiment

In the following, the seventh embodiment of the present invention willbe described with reference to figures.

FIG. 19 is a block diagram of a digital watermarking system to which thepresent invention relates. FIG. 19 shows a similar configuration to thatshown in FIG. 1. The difference is that FIG. 19 shows a digitalwatermark data reconstitution apparatus 108 which is an essential partof the present invention. The digital watermark data reconstitutionapparatus 108 is provided in the watermark embedding apparatus 106. Inthe system, a digital watermark data sequence is read from thewatermarked digital data contents 105 by using the watermark readingapparatus 106. Then, the digital watermark data sequence is processed inthe digital watermark data reconstitution apparatus 108 so that the readdigital watermark data 107 is obtained.

In the following, the process for reconstituting the digital watermarkdata is described in detail.

FIG. 20 is a block diagram of the watermark reading apparatus 106. Thedigital watermark data reconstitution apparatus 108 provided in thewatermark reading apparatus 106 obtains the probability q that bit 1 isread when any 1 bit watermark sequence is read from a whole watermarkarea beforehand by using the watermark reading apparatus 106.

Specifically, assuming a 1 bit watermark sequence reading part 501, thepart 501 reads the watermark sequence 1 bit by 1 bit from all elementsof the whole watermark area (a broken line L1), and calculates the ratioof the number of bit 1 to the number of all trials.

In the embodiment, the reading probability of bit 1 and the number ofbit 1 are obtained. However, it is possible that the reading probabilityof bit 0 and the number of bit 0 are obtained. Basically, there is nodifference between the former and the latter. The difference is only onimplementation.

Accordingly, the probabilities of detecting bit 0 and 1 when reading 1bit at random in the watermark area by using the digital watermarkingalgorithm is calculated to be 1-q and q respectively.

The n bit watermark sequence reading part 502 reads the digitalwatermark data sequence from the watermarked digital data contents forthe number of total times of embedding digital watermark data.

Here, digital watermark data is defined as b₀,b₁, . . . , b_(m-1), b_(i)ε{0, 1}, i<m (m bit length), the repeating number of embedding ith bitof the digital watermark data in the digital data contents is defined asn_(i), the read watermark sequence is defined as$b_{0,0}^{\prime},b_{0,1}^{\prime},{\ldots\quad b_{0,{{n\quad 0} - 1}}^{\prime}},b_{1,0}^{\prime},b_{1,1}^{\prime},{\ldots\quad b_{1,{{n\quad 1} - 1}}^{\prime}},\ldots\quad,b_{{m - 1},0}^{\prime},b_{{m - 1},1}^{\prime},{{\ldots\quad b_{{m - 1},{{n\quad m} - 1 - 1}}^{\prime}\quad b_{i,j}} \in {\{ {0,1} \}\quad{( {\sum\limits_{r = 0}^{m - 1}{n_{r}\quad{bit}\quad{length}}} ).}}}$

The data reconstitution apparatus 108 receives a subsequence of thedigital watermark data sequence one after another from a subsequencecorresponding to 0th digital watermark data to a subsequencecorresponding to (m-1)th digital watermark data (a solid line L2).

Next, the method for reconstituting ith bit of the digital watermarkdata will be described concretely.

When n_(i) bits of digital watermark data sequence is read at randomfrom the watermark area, the probability P(x=k) of k ‘1’ bits appearingin the n_(i) bit sequence is represented by the binary distributiondensity functionP(x=k)=n _(i) C _(k) q ^(k)·(1-q)^(ni-k)   (1)and the distribution function of that, F(x), is $\begin{matrix}{{F(x)} = {\sum\limits_{k = 0}^{x}{n_{i}C_{k}{q^{k} \cdot ( {1 - q} )^{{ni} - k}}\quad{( {0 \leqq x \leqq n_{i}} ).}}}} & (2)\end{matrix}$Here, n_(i)C_(k) is the number of combinations when selecting k out ofn_(i).

Setting a reliability threshold value α (½≦α1) of the digital watermarkdata, the number of bit 1 included in a subsequence b′_(i,0), b′_(i,1),. . . b′_(i,ni-1) corresponding to ith digital watermark data iscalculated by$k_{i} = {\sum\limits_{r = 0}^{{n\quad i} - 1}\quad{b_{i,r}^{\prime}.}}$Then, digital watermark data is determined in the following way by usingthe formula (2): $\begin{matrix}{b_{i} = \lbrack \begin{matrix}0 & {{{when}\quad 0} \leqq {F( k_{i} )} \leqq {1 - \alpha}} \\1 & {{{when}\quad\alpha} \leqq {F( k_{i} )} \leqq 1} \\{{{unknown}\quad{or}}\quad} & {{{{when}\quad 1} - \alpha} < {F( k_{i} )} < \alpha} \\{{not}\quad{present}} & \quad\end{matrix} } & (3)\end{matrix}$

Viewing from a different angle, when determining by the number of bit 1included in the watermark sequence n_(i), if the largest integer x₀ thatsatisfies 0≦F(x =x₀)≦1−α and the smallest integer x₁ that satisfiesα≦F(x=x₁)≦1 are assumed to be threshold values, the digital watermarkdata is judged as shown in FIG. 21 such that if the number of 1 in n_(i)is equal to or smaller than x₀, the digital watermark data is 0, andthat if the number of 1 is equal to or larger than x₁, the digitalwatermark data is 1.

The horizontal axis of FIG. 21 represents the number of bit 1 includedin the watermark sequence, and the vertical axis represents frequency ofthe corresponding number. As for unwatermarked digital data contents,the frequency that bit 1 appears in a bit sequence read at random fromthe digital data contents becomes binary distribution. Thus, the peak ofthe frequency is at the half point of the number of bits. On the otherhand, as for watermarked contents, in the subsequence n_(i) in which bit0 is embedded as digital watermark data, the frequency of bit 1 is 0 ifthere is no degradation and it is a small number which is equal to orsmaller than x₀ even if there is degradation. In the subsequence n_(i)in which bit 1 is embedded as digital watermark data, the frequency ofbit 1 is n1 if there is no degradation and it is a large number which isequal to or larger than x₁ even if there is degradation. In this way,the distribution of the frequency of bit 1 or bit 0 in the watermarkedsequence is leaning to one side from the center of the binarydistribution. The present invention uses the lean for reconstitutingdigital watermark data from the read watermark sequence.

Depending on a watermarking system, a following method can be used. Thatis, reconstituted digital watermark data is obtained by using the biasfrom the central value of the distribution P(x) of the watermarksequence extracted from digital data contents 105. Next, the probabilityof appearing the read watermark sequence is calculated by the formula(2). Then, if the reconstituted digital watermark data is 1, F(k_(i))can be added to watermark dada as the reliability, and, if thereconstituted digital watermark data is 0, 1-F(k_(i)) can be added. Thereliability F(k_(i)) and 1-F(k_(i)) of the digital watermark data isobtained from the bias of appearance probability of the digitalwatermark data in the binary distribution of appearance probability ofeach bit of 1 bit sequence extracted at random from digital datacontents.

FIG. 22 shows a concept in which the length of the digital watermarkdata is extended to m bits.

The digital watermark data reconstitution apparatus 108 outputs thereconstituted digital watermark data b₀, b₁, . . . , b_(m-1) as readdigital watermark data 107.

FIG. 23 is a flowchart showing the above-mentioned process. The processwill be described in the following with reference to FIG. 23.

Watermarked digital data contents 105 and key data which is necessaryfor reading digital watermark data is input, and a digital watermarkdata sequence is extracted with respect to each bit value in step 1.Then, a threshold value α of the reliability is set in step 2, and aprobability q that bit 1 appears when 1 bit of digital watermark data isread at random from the whole watermark area is obtained in step 3.Then, a binary distribution function F(x) which represents probabilitythat x bits of 1 are included in the bit sequence is obtained from theprobability q and the repeating number n_(i) of each bit of digitalwatermark data in step 4.

Then, 0 is assigned to i which distinguish a subsequence of the digitalwatermark data sequence in step 5. Next, the number of bit 1 in thesubsequence is obtained as$k_{i} = {\sum\limits_{r = 0}^{{n\quad i} - 1}\quad b_{i,r}^{\prime}}$and the appearance probability F(k_(i)) is obtained, then it isdetermined whether F(k_(i)) is equal to or less than 1−α in step 6. IfF(_(i))≦1−α, the digital watermark data w′_(i) is reconstituted as 0 instep 7. Then, i is incremented by 1 in step 8, and the process goes backto step 6 if i<m in step 9. If F(k_(i))≦1−α is not true in step 6, it ischecked whether F(k_(i))≧α is true in step 10. If F(k_(i))≧α, thedigital watermark data w_(i) is reconstituted as 1 in step 11, and theprocess goes to step 8. If F(k_(i))≧α is not true in step 10, theprocess ends by determining as there is no watermark or the presence orabsence is unknown in step 12. If i is more than n_(i) in step 9, areconstituted watermark sequence {w′_(i)} is output. In the aboveprocess, the reading process in step 1 can be carried out between step 4and step 5. In step 6, it is checked whether 1-F(k_(i)) is more than α.

In the seventh embodiment, it is assumed that there is no bias in thedistribution represented by formula (1), that is, q≅½.

When the embedding number ni of each bit of digital watermark data isadequate for obtaining a statistical characteristic, it becomes q≅½generally. However, since the value of q depends on characteristics ofan watermarking algorithm and digital data contents, q may take a valuedeviating largely from ½ in some rare cases. A method for solving thisproblem will be described in a eighth embodiment.

Eighth Embodiment

In the following, the eighth embodiment will be described. FIG. 24 is ablock diagram of a watermarking system of the ninth embodiment.

The watermark embedding apparatus 102 embeds digital watermark data 101in digital data contents 103. At the time, when embedding each bit valuen_(i) times repeatedly, watermark sequence is modulated and embedded inthe digital data contents 103. The modulation is carried out by apseudo-random sequence generator (A) 601 which is provided in thewatermark embedding apparatus 102.

For example, when assuming the embedding sequence as b_(0,0), b_(0,1), .. . b_(0,n0 −1), b_(1,0), b_(1,1), . . . b_(1 ,n1-1), . . . , b_(m-1,0),b_(m-1,1), . . . b_(m-1,nm-1 −1) b_(i,j) ε{0, 1}, and the pseudo-randomsequence as r_(i,0), r_(i,1), . . . r_(i,ni-1) b_(i,j) ε{0, 1}, theembedding sequence is modulated to

-   -   m_(i,0), m_(i,1), . . . m_(i, ni-1)    -   m_(i,j)=b_(i,j)(+)r_(i,j)        by the pseudo-random sequence. A(+)B represents XOR of A and B.

According to the above-mentioned process, the same pseudo-randomsequence is necessary for digital watermark data reading.

For example, if 1 bit watermark sequence is read by using an M-sequenceas the pseudo-random sequence, it becomes q≅½. Therefore, the presentinvention can be applicable without depending on the watermarkingalgorithm and digital data contents.

When digital watermark data reading, demodulation is carried out asb′_(i,j)=m_(i,j)(+)r_(i,j) by using a pseudo-random sequence generator(B) 602 which is provided in the watermark reading apparatus 106.

Here, the pseudo-random sequence generator (A) 601 and the pseudo-randomsequence generator (B) 602 needs to be implemented such that both of thegenerators generate the same pseudo-random sequence.

Watermark data is reconstituted with the method of the seventhembodiment from the watermark sequence b′_(0,0), b′_(0,1), . . .b′_(0,n0-1), b′_(1,1), . . . b′_(1,n1-1), . . . , b′_(m-1,0),b′_(m-1,1), . . . b′_(m-1,nm-1 −1) b_(i,j) ε{0, 1} obtained by thedemodulation.

Since it is considered that the appearance probability q of bit 1 in thewatermark sequence can be approximated by the binary distributionregardless of the presence or absence of modulation, there is noinfluence on the distribution of the density function (1) due to themodulation shown in this embodiment.

In addition, q=½ can be assumed in implementation, that is, no processis necessary for obtaining q. Therefore, the amount of processing thatis required for watermark reconstitution thus becomes the same as thatfor majority decision processing. Thus, the reconstitution processbecomes faster.

Ninth Embodiment

In the following, a ninth embodiment will be described. In the ninthembodiment, an example will be described showing concrete values on thebasis of the seventh embodiment and the eighth embodiment. In thisembodiment, it is assumed that digital watermark data is 1 bit, therepeating number n of embedding is 127 and the probability q that bit 1is read when reading 1 bit watermark sequence at random from the wholewatermark area is ½. If the threshold value α is 0.99999 (which means99.999%), x₀ in FIG. 21 is 36 and x₁ is 90. That is to say, according tothe present invention, under the above-mentioned condition, digitalwatermark data is judged as bit 0 if the number of ‘1’ appeared in thewatermark sequence (n bits) is equal to or less than 36, and it isjudged as bit 1 if the number of ‘1’ appeared in the watermark sequence(n bits) is equal to or more than 90, and it is judged that there is nowatermark data or the presence or absence is unknown in other cases. Ifit is judged that there is digital watermark data, the correctness ofmore than 99.999% can be ensured.

Tenth Embodiment

A tenth embodiment will be described in the following. According to theembodiment shown in FIG. 23, as is understood from the above-mentionedprocedure, if even the reliability of only 1 bit is not obtained, thatis, if F(k_(i)) or 1-F(k_(i)) is less than α, the reconstitution of thedigital watermark data becomes impossible because it is judged thatthere is no digital watermark data or the presence or absence isunknown. The tenth embodiment solves the problem. In this case, it isassumed that the repeating number of embedding each bit of digitalwatermark data is the same value n.

The method for reconstituting digital watermark data w₀, w₁, . . . ,w_(m-1) from watermark sequence b′_(0,0), b′_(0,1), . . . b′_(0,n0-1),b′_(1,0), b′_(1,1), . . . , b′_(m,0), b′_(m,1), . . . b′_(m,n-1) whichis read from digital data contents will be described in the followingwith reference to FIG. 25.

The watermark sequence is read with respect to each bit value from thedigital data contents and key data necessary for digital watermark datareading in step 1.

The threshold value α (½<α≦1) of the reliability is set in step 2. Forexample, if the reliability of read digital watermark data needs to beequal to or more than 99%, it is set as α=0.99.

The probability q of bit ‘1’ when 1 bit of the watermark sequence isread at random from the whole watermark area of watermarked digital datacontents is obtained beforehand in step 3. The appearance probabilitiesof bits ‘0’ and ‘1’ are calculated as 1-q and q respectively.

The probability that x bits of ‘1’ are included in the watermarksequence of each bit data of digital watermark data are obtained as${F(x)} = {\sum\limits_{j = 0}^{x}\quad{{{}_{}^{}{}_{}^{}}{q^{j} \cdot ( {1 - q} )^{n - j}}}}$by using the binary distribution function in step 4.

It is checked in step 5 that the probability that n bit digitalwatermark data sequence is digital watermark data exceeds the thresholdvalue α. Specifically, it is checked whether the following formula (4)is satisfied. $\begin{matrix}{{F( {\frac{\sum\limits_{i = 0}^{m - 1}\quad{{{\sum\limits_{j = 0}^{n - 1}\quad b_{i,j}^{\prime}} - \frac{n}{2}}}}{m} + \frac{n}{2}} )} \geq \alpha} & (4)\end{matrix}$Here, |a| represents the absolute value of a.${\sum\limits_{j = 0}^{n - 1}\quad b_{i,j}} - \frac{n}{2}$represents the bias from the center of the binary distribution of thenumber of bit ‘1’ in the n bit watermark sequence.${\sum\limits_{i = 0}^{m - 1}\quad{{of}{\quad\quad}{\sum\limits_{j = 0}^{n - 1}\quad b_{i,j}}}} - \frac{n}{2}$divided by m represents the average for the m bits of the whole digitalwatermark data. n/2 represents the center of the binary distribution.

If the formula (4) is true, it is judged that there is digital watermarkdata. Thus, in each n bit watermark sequence of m digital watermark datasequences, digital watermark data is reconstituted by a majoritydecision processing.

Specifically, if it is judged that there is digital watermark data,digital watermark data is reconstituted in the following way in step 6.$\begin{matrix}{{{For}\quad{all}\quad i\quad( {0 \leqq i < m} )},} \\{{{{{when}\quad{\sum\limits_{j = 0}^{n - 1}\quad b_{i,j}}} < {\frac{n}{2}\text{:}\quad w_{i}^{\prime}}} = 0},} \\{{{{when}\quad{\sum\limits_{j = 0}^{n - 1}\quad b_{i,j}}} \geq {\frac{n}{2}\text{:}\quad w_{i}^{\prime}}} = 1.}\end{matrix}$

This process is carried out by steps 6-1-6-7 in FIG. 25.${{{If}\quad{F( {\frac{\sum\limits_{i = 0}^{m - 1}\quad{{{\sum\limits_{j = 0}^{n - 1}\quad b_{i,j}} - \frac{n}{2}}}}{m} + \frac{n}{2}} )}} < \alpha},$it is judged that there is no watermark data or the presence or absenceis unknown. A following formula (5) can be used instead of the formula(4). $\begin{matrix}{{F( {\frac{n}{2} - \frac{\sum\limits_{i = 0}^{m - 1}\quad{{{\sum\limits_{j = 0}^{n - 1}\quad b_{i,j}^{\prime}} - \frac{n}{2}}}}{m}} )} \leq {1 - \alpha}} & (5)\end{matrix}$

If the formula (5) is not true, it is judged that there is no watermarkdata or the presence or absence unknown.

According to the tenth embodiment, statistical processing for wholewatermark sequence is carried out so as to judge the presence or absenceof watermark by using the formula (4) or the formula (5). If it isjudged that there is digital watermark data, the reconstitution iscarried out by the majority decision processing. Therefore, even ifthere is one bit of low reliability, digital watermark data can bereconstituted.

In FIG. 25, the step 1 can be carried out between the steps 4 and 5.

The tenth embodiment may use the pseudo-random sequence which isdescribed in the eighth embodiment. Specifically, watermark embedding iscarried out by modulating digital watermark data sequence with thepseudo-random sequence. When reconstituting, the read digital watermarkdata sequence is demodulated by the pseudo-random sequence, then thejudgment by the formula (4) is performed. If the result is more than αand there is digital watermark data, the reconstitution process of themajority decision is performed on the demodulated sequence, which is thesame process as the step 6 of the eleventh embodiment. The whole processis shown in FIG. 26, adding the same reference symbol to thecorresponding part shown in FIG. 25. In the example, the pseudo-randomsequence {r_(i,j)} is generated from key data ‘Key’ and the process goesto step 2 in step 8. Next to step 4, watermark sequence is demodulatedwith the pseudo-random sequence {r_(i,j)} in step 9. The watermark bitb′_(i,j) in the formula (4) in step 5 is a bit which is demodulated instep 9. Also, the majority decision processing in step 6 is performed onb′_(i,j).

Eleventh Embodiment

In the following, a eleventh embodiment will be described.

Since digital watermark data is dispersed by the pseudo-random sequence,when q is approximated to ½, the presence or the absence of watermarkdata in the watermark sequence can be judged as follows.

The probability that x bits of ‘1’ (a number x of ‘1’ bits) are includedin the n bit watermark sequence which constitutes each bit of digitalwatermark data is represented as${F(x)} = {\sum\limits_{j = 0}^{x}\quad{{{}_{}^{}{}_{}^{}}( {1/2^{n}} )}}$by using the binary distribution function. Accordingly, by obtaining thesmallest integer x₁ which satisfies F(x=x₁)≧α, the demodulated sequenceof the step 5 in the tenth embodiment can be judged with the followingformula (6). $\begin{matrix}{{\frac{\sum\limits_{i = 0}^{m - 1}\quad{{{\sum\limits_{j = 0}^{n - 1}\quad b_{i,j}^{\prime}} - \frac{n}{2}}}}{m} + \frac{n}{2}} \geq x_{1}} & (6)\end{matrix}$In this case, the amount of processing can be reduced to the same levelas that of the majority decision processing.

The judgment is equivalent to a judgment for judging whether the averageof the bias from the center n/2 of the binary distribution of thewatermark sequence is equal to or more than x₁.

If the formula (6) is true and it is judged that there is digitalwatermark data, the majority decision process is performed on thewatermark sequence which is demodulated by the pseudo-random sequence inthe following way. $\begin{matrix}{{{For}\quad{all}\quad i\quad( {0 \leqq i < m} )},} \\{{{{{when}\quad{\sum\limits_{j = 0}^{n - 1}\quad b_{i,j}^{\prime}}} < {\frac{n}{2}\text{:}\quad w_{i}^{\prime}}} = 0},} \\{{{{when}\quad{\sum\limits_{j = 0}^{n - 1}\quad b_{i,j}^{\prime}}} > {\frac{n}{2}\text{:}\quad w_{i}^{\prime}}} = 1}\end{matrix}$Then, the digital watermark data is reconstituted.${{{{If}\quad\frac{\sum\limits_{i = 0}^{m - 1}\quad{{{\sum\limits_{j = 0}^{n - 1}\quad b_{i,j}^{\prime}} - \frac{n}{2}}}}{m}} + \frac{n}{2}} < x_{1}},$it is judged that there is no watermark data or the presence or absenceis unknown.

In the above process, it is possible to use the maximum integer X₀ whichsatisfies F(x=x₀)≦1−α instead of the minimum integer x₁ which satisfiesF(x=x₁)≧α. In this case, a formula for judging the presence or absenceof watermark is shown below as a formula (7). $\begin{matrix}{{\frac{n}{2} - \frac{\sum\limits_{i = 0}^{m - 1}\quad{{{\sum\limits_{j = 0}^{n - 1}\quad b_{i,j}^{\prime}} - \frac{n}{2}}}}{m}} \leq x_{0}} & (7)\end{matrix}$If the left part of the formula is more than x₀, it is judged that thereis no watermark data or the presence or absence is unknown.

Twelfth Embodiment

In the following, a twelfth embodiment of the present invention will bedescribed.

When it is judged that there is digital watermark data by the formula(4), the digital watermark data is reconstituted by the above-mentionedmajority decision process. At the same time, the reliability of thereconstituted watermark sequence as a whole is calculated as$F( {\frac{\sum\limits_{i = 0}^{m - 1}\quad{{{\sum\limits_{j = 0}^{n - 1}\quad b_{i,j}^{\prime}} - \frac{n}{2}}}}{m} + \frac{n}{2}} )$and it is output.

Similarly, when it is judged that there is digital watermark data by theformula (5) and the digital watermark data is reconstituted, thereliability of the reconstituted digital watermark data sequence as awhole is calculated as$F( {\frac{n}{2} - \frac{\sum\limits_{i = 0}^{m - 1}\quad{{{\sum\limits_{j = 0}^{n - 1}\quad b_{i,j}^{\prime}} - \frac{n}{2}}}}{m}} )$and it is output.

When it is judged that there is digital watermark data by the formula(6), the digital watermark data is reconstituted by the above-mentionedmajority decision process. At the same time, the reliability of thereconstituted watermark sequence as a whole is calculated as$F( {\frac{\sum\limits_{i = 0}^{m - 1}\quad{{{\sum\limits_{j = 0}^{n - 1}\quad b_{i,j}^{\prime}} - \frac{n}{2}}}}{m} + \frac{n}{2}} )$and it is output.

Similarly, when it is judged that there is digital watermark data by theformula (7), the reliability of the digital watermark data as a whole iscalculated as$F( {\frac{n}{2} - \frac{\sum\limits_{i = 0}^{m - 1}\quad{{{\sum\limits_{j = 0}^{n - 1}\quad b_{i,j}^{\prime}} - \frac{n}{2}}}}{m}} )$and it is output.

In the above-mentioned seventh-twelfth embodiments, the readingprobability of bit 1 and the number of bit 1 are obtained. However, itis possible that the reading probability of bit 0 and the number of bit0 are obtained. Basically, there is no difference between the former andthe latter. The difference is only on implementation.

In the following, examples of experiments will be shown. In thefollowing experiments, an image of “lena” which has 128×128 pixels isused as a test image, and the threshold value α of the reliability isassumed to be 0.999999.

(First Experiment)

In this experiment, 1 bit digital watermark data ‘1’ was embedded 127times repeatedly using key data ‘50,000’, and the watermark sequence wasread with various key data. FIG. 27 shows the number of bit ‘1’ in theread watermark sequence corresponding to the key data. In FIG. 27, thevertical axis shows the number of bit ‘1’ in the read watermarksequence, and the horizontal axis shows the key data value. In thisexperiment, the appearance frequency of bit ‘1’ in the watermark area Awas q=0.492247.

When correct key data (50,000) is used, it is judged that digitalwatermark data is ‘1’ with 99.9999% correctness since the number of bit‘1’ is more than the threshold value x₁ for judging the presence ofwatermark. When incorrect key data is used, it is judged that there isno watermark data or the presence or absence is unknown.

(Second Experiment)

In the second experiment, a watermark sequence which was modulated witha 7 stage M-sequence (initial state is 64) was embedded, and a similarexperiment as the first experiment was carried out with various key dataand M-sequences of various initial states. The result is shown in FIG.28. By carrying out the modulation, the value of q becomes 0.500000 from0.492247, and the variance becomes 31.718777 from 31.008265. Thus, thevalues are almost not changed from those of the first experiment. It isonly when correct key data and correct pseudo-random sequence are usedthat digital watermark data can be read. In addition, when the watermarksequence is embedded in half data of the watermark area A, q=0.741547with the modulation and q=0.499768 without the modulation.

The effects of the present invention corresponding to the second objectis as follows.

(1) There are following effects by judging digital watermark data on thebasis of the binary distribution in statistics:

-   -   The probabilities of following cases can be evaluated        quantitatively. The cases are: digital data contents which do        not contain digital watermark data are wrongly judged as        containing digital watermark data, and incorrect digital        watermark data is read from watermarked digital data contents.        In addition, the probability can be suppressed within 2(1−α) by        using the reliability threshold α of digital watermark data.

(2) There are following effects by modulating digital watermark data bya pseudo-random sequence before embedding the digital watermark data:

-   -   The bias of the probability q of reading bit ‘1’ when 1 bit        watermark sequence is read at random from the whole watermark        area.    -   It becomes difficult to detect the presence or absence of        watermark data and the value from the bias of q without the        correct key data and the pseudo-random sequence, the key data        being necessary for reading digital watermark data and the        pseudo-random sequence being necessary for demodulating read        watermark sequence. It can strengthen security which is an        important element for the digital watermarking system.    -   In an implementation, since it can be assumed to be q=½, the        amount of processing that is required for watermark        reconstitution becomes the same as that for majority decision        processing. Thus, the speed of the processing becomes higher.

α is an index which represents a lower limit of the correctness rate ofread digital watermark data, and is manageable in the digitalwatermarking system. Therefor, the method of using α is superior to aconventional method of showing the correctness rate of read digitalwatermark data to a user.

According to the seventh embodiment, if there is even one bit of lowreliability in digital watermark data {w′_(i)}, it is judged that thereis no watermark data or the presence or absence is unknown. However,even in the case, according to the eleventh

-   -   thirteenth embodiments, the reliability of digital watermark        data can be evaluated quantitatively, the probability for        reading digital watermark data incorrectly can be suppressed        within 2(1−α), and the digital watermark data can be        reconstituted. In the tenth-twelfth embodiments, the whole        digital watermark data is statistically processed by modifying        the formula for judging the presence or absence of digital        watermark data, since digital watermark data can be        reconstituted in many cases, when watermark sequence {b′_(i,j)},        (0≦i<m,0j≦n) is seen statistically as a whole.

In addition, according to the seventh embodiment,$F( {\sum\limits_{j = 0}^{n - 1}\quad b_{i,j}^{\prime}} )$needs to be calculated with the distribution function F(x) of the binarydistribution for all i to reconstitute digital watermark data fromwatermark sequence. On the other hand, according to the tenth-twelfthembodiments, only one calculation using the distribution function isnecessary so that the amount of processing can be reduced.

The present invention becomes more effective in combination with anerror correction code. That is, when a part of bits in digital watermarkdata is intensively corrupted, it is judged that only the part of bitsis unknown and other bit data is in high correctness rate. Therefore,correct data can be read by correcting only the corrupted bit data.

In the present invention corresponding to the second object, theabove-mentioned processes can be constituted by programs which can bestored in a computer readable medium. Therefore, digital watermarkingprocessing of the present invention can be carried out with a computersuch as one shown in FIG. 17. Additionally, the watermarking apparatusof the present invention can be realized by an integrated circuit suchas one shown in FIG. 18.

In the following, the present invention corresponding to the thirdobject will be described.

In the first place, the conventional digital watermark reading methodwill be further described in order to clarify the feature of the presentinvention corresponding to the first objective. The conventional methodis based on hard decisions on binary coding in code theory, which isshown in FIG. 29. With respect to the watermark reading method based onhard decisions on binary coding, if almost all watermarked contents areembedded within a same range (shown as the diagonally shaded area), theperformance is enough.

However, according to the conventional watermark reading method, thereis a following problem. FIG. 30 shows a graph showing how MPEG-1 codingchanges ‘1’ data bit, specifically the graph shows occurrence frequencywith respect to change amount of a DCT coefficient value by 1.5 MbpsMPEG-1 coding. As shown in FIG. 30, there is a case in which aconsiderable amount of watermarked data appears in the vicinity of theboundary of the reading bit value (which is shown in two dotted circlesa and a′). As a result, it becomes difficult to separate noise from thewatermarked data. In addition, there is a possibility that a digitalwatermark data value which is read becomes reversed with respect to theembedded digital watermark data.

In order to avoid the problem, two measures are conceivable. Firstmeasure is to raise the data diffusion rate by increasing the number oftimes the data is embedded. Second measure is to increase the watermarkembedding strength. Neither of these measures is a true solution becausethe first one may reduce the relative amount of embedded data and thesecond one may degrade the image. Accordingly, the present inventionadopts soft decision rather than hard decision. In the following, ageneral description of the present invention will be given.

FIG. 31 is a diagram of a principle of the present inventioncorresponding to the third object. As shown in the figure, a watermarksequence and the reliability is obtained in step 1, and, then, mostlikely digital watermark data is reconstituted based on the watermarksequence and the reliability in step 2.

FIG. 32 is a diagram showing a principle of a digital watermark readingapparatus of the present invention. As shown in FIG. 32, the digitalwatermark reading apparatus includes a digital watermark sequenceobtaining part 1 and reconstitution part 2. The digital watermarksequence obtaining part 1 obtains the most likely digital watermarksequence and the reliability by carrying out soft decisions of codingtheory using a weight function, and the reconstitution part 2reconstitutes digital watermark data on the basis of the most likelydigital watermark sequence and the reliability.

Inferring from the frequency plot shown in FIG. 30, it is easy to detectthe digital watermark data sequence correctly if the repeating number ofembedding is large enough. However, if a sufficiently large repeatingnumber can not be obtained in actual practice, it becomes difficult todetect the desired digital watermark data sequence, thus filtering forwatermarked content data becomes important. For example, concerning datawhich exists in the dotted circle in FIG. 30, it is difficult todetermine whether the data is watermarked content data or noise. Thus,it is needed to separate watermarked content data from noiseeffectively. For that purpose, according to the present invention,weights are assigned to the digital watermark data sequence by usingsoft decisions of coding theory. Specifically, distribution ofwatermarked content data is predicted, then digital watermark data isreconstituted from a digital watermark data sequence to which acorresponding distribution value is added as the weight.

Accordingly, the watermarked content data can be separated from noise.Thus, error bits included in the digital watermark data sequence can bereduced, thereby a success rate of reading digital watermark dataimproves as compared with the above-mentioned conventional methods.According to the present invention, it becomes possible to seesignificant distribution bias in the watermark content data when therepeating number of embedding digital watermark data is small.

In the following, the present invention corresponding to the thirdobject will be described in detail.

First, the operation of the digital watermark reading apparatus 106 willbe described. FIG. 33 is a diagram for explaining the operation. Asshown in FIG. 33, the process according to the present inventioncorresponds to the process shown in FIG. 5 in which steps 240-250 areimproved.

As shown in FIG. 33, in the digital watermark reading apparatus 106,when reading digital watermark,$\lbrack {{{{v\lbrack X\rbrack}\lbrack Y\rbrack} = {{{weight}( \frac{f^{\prime}\lbrack Y\rbrack}{q\lbrack i\rbrack} )} - {Z \times \{ {( {Z\quad{mod}\quad 2} ) - 1} \}}}},\quad{{for}\quad{all}\quad i\quad( {0 \leq i < {\lfloor \frac{m}{n} \rfloor \cdot n}} )},} $by using frequency coefficient quantization width q[0],q[1], . . .,q[m-1]. Here,${X = \lfloor \frac{i}{t} \rfloor},\quad{Y = {i\quad{mod}\quad t}},\quad{Z = {\lfloor {\frac{f^{\prime}\lbrack i\rbrack}{q\lbrack i\rbrack} + \frac{1}{2}} \rfloor.}}$The function weight will be described later.

In the process for reconstituting digital watermark data by performingstatistical processing on a digital watermark data sequence, forexample, ${W\lbrack j\rbrack} = \{ \begin{matrix}1 & {{\sum\limits_{k = 0}^{t - 1}\quad{{v\lbrack j\rbrack}\lbrack k\rbrack}} \geq 0} & \quad \\\quad & \quad & ( {0 \leqq j < n} ) \\0 & {{\sum\limits_{k = 0}^{t - 1}\quad{{v\lbrack j\rbrack}\lbrack k\rbrack}} < 0} & \quad\end{matrix} $is used for the reconstitution.

Thirteenth Embodiment

In the following, a thirteenth embodiment of the present invention willbe described. In the following example, the digital watermark readingprocess based on quantization in the digital watermark reading apparatus106 will be described.

According to the thirteenth embodiment of the present invention, thedigital watermark embedding process is not changed from the conventionalmethod. On the other hand, the digital watermark reading process ismodified in order to improve digital watermark reading performance.

Here, let digital watermark data to be embedded in contents be w₀,w₁, .. . ,w_(n-1),w_(i) ε{−1, 1}, 0≦i≦n-1, and let a data set in whichdigital watermark data is embedded be {d_(0,0),d_(0,1), . . .,d_(0,m-1), d_(1,0),d_(1,1), . . . ,d_(1,m-1), . . ,d_(n-1,1), . . .,d_(n-1,m-1)}. Let a quantization value used for quantize datad_(i,j)(0≦i≦n-1,0≦j≦m-1) be q_(i,j). Each bit data w_(i) of digitalwatermark data is embedded m times repeatedly. The digital watermarkembedding process based on quantization is assumed to be a process inthe following.${ {{ {{ {{{For}\quad{all}\quad i\quad{and}\quad j\quad( {{0 \leqq i \leqq {n - 1}},\quad{0 \leqq j \leqq {m - 1}}} )}i} )\quad{If}\quad\lfloor {\frac{d_{i,j}}{q_{i,j}} + \frac{1}{2}} \rfloor{mod}\quad 2\quad{is}\quad{equal}\quad{to}\quad w_{i}},{d_{i,j}\quad{is}\quad{changed}\quad{to}\quad\lfloor {\frac{d_{i,j}}{q_{i,j}} + \frac{1}{2}} \rfloor \times {q_{i,j}.{ii}}}} ){\quad\quad}{If}\quad\lfloor {\frac{d_{i,j}}{q_{i,j}} + \frac{1}{2}} \rfloor{mod}\quad 2\quad{is}\quad{different}\quad{from}\quad w_{i}\quad{and}\quad\lfloor {\frac{d_{i,j}}{q_{i,j}} + \frac{1}{2}} \rfloor\quad{is}\quad{equal}\quad{to}\quad\lfloor \frac{d_{i,j}}{q_{i,j}} \rfloor},{d_{i,j}\quad{is}\quad{changed}\quad{to}\quad( \quad{\lfloor {\frac{d_{i,j}}{q_{i,j}} + \frac{1}{2}} \rfloor + 1} ) \times {q_{i,j}.{iii}}}}\quad )\quad{If}\quad\lfloor {\frac{d_{i,j}}{q_{i,j}} + \frac{1}{2}} \rfloor{mod}\quad 2\quad{is}\quad{different}\quad{from}\quad w_{i}\quad{and}\quad\lfloor {\frac{d_{i,j}}{q_{i,j}} + \frac{1}{2}} \rfloor\quad{is}\quad{different}\quad{from}\quad\lfloor \frac{d_{i,j}}{q_{i,j}} \rfloor},{d_{i,j}\quad{is}\quad{changed}\quad{to}\quad( \quad{\lfloor {\frac{d_{i,j}}{q_{i,j}} + \frac{1}{2}} \rfloor - 1} ) \times {q_{i,j}.}}$Here, └x┘ is a maximum number which does not exceed x. “x mod y”represents the remainder of x divided by y.

The present invention is not only applicable to the contents in whichdigital watermark data is embedded in the above-mentioned way but alsoapplicable to other contents in which digital watermark data is embeddedin other equivalent way.

In the following, the operation of the digital watermark readingapparatus 106 will be described in detail.

According to a following process, a watermark sequence {{tilde over(w)}_(0,0),{tilde over (w)}_(0,1), . . . ,{tilde over(w)}_(0,m-1),{tilde over (w)}_(1,0),{tilde over (w)}_(1,1), . . .,{tilde over (w)}_(1,m-1), . . . ,{tilde over (w)}_(n-1,0),{tilde over(w)}_(n-1,1), . . . ,{tilde over (w)}_(n-1,m-1)} is read from a set ofdata values {{tilde over (d)}_(0,0),{tilde over (d)}_(0,1), . . .,{tilde over (d)}_(0,m-1),{tilde over (d)}_(1,0),{tilde over (d)}_(1,1),. . . ,{tilde over (d)}_(1,m-1), . . . ,{tilde over (d)}_(n-1,0),{tildeover (d)}_(n-1,1), . . . ,{tilde over (d)}_(n-1,m-1)} of the watermarkeddigital data contents 105 in which digital watermark data is embedded.For  all  i  and  j  (0 ≦ i ≦ n − 1,  0 ≦ j ≦ m − 1)$n_{i,j} = {\lfloor {\frac{{\overset{\sim}{d}}_{i,j}}{q_{i,j}} + \frac{1}{2}} \rfloor\quad{and}}$${\overset{\sim}{w}}_{i,j} = {{{weight}( {\frac{{\overset{\sim}{d}}_{i,j}}{q_{i,j}} - n_{i,j}} )} \times {\{ {{( {n_{i,j}\quad{mod}{\quad\quad}2} ) \times 2} - 1} \}.}}$

Here, weight(x) (the domain is${{- \frac{1}{2}} \leq x \leq \frac{1}{2}},$and the range is equal to or more than 0. The function weight(x) will becalled a weight function hereinafter) is a function which assignsweights to a read watermark sequence. By adopting a function which takesa large value in the vicinity of the central value (in the vicinity ofthe dotted vertical axis in FIG. 30) and takes a small value in thevicinity of the boundary of the bit value (in the dotted circle in FIG.30), it becomes possible to separate effective watermark data sequencefrom noise.

Of course, it is possible to adopt a stretched weight(x) function inwhich the domain and the region is not limited. However, in the case, itis necessary to change the above mentioned formula to some extent.

Contents in which digital watermark data is embedded by digitalwatermark embedding processing is degraded due to data compression,media processing and the like. Thus, a watermark embedded data value{tilde over (d)}_(i,j) deviates in some degree from a value d_(i,j) ofimmediately after being embedded. Therefore, it is desirable to adopt afollowing function as the weight function. The function can be obtainedsuch that the distribution of the ratio$\frac{{\overset{\sim}{d}}_{i,j} - d}{q_{i,j}}$of the amount of the deviation between d_(i,j) and {tilde over(d)}_(i,j) to the quantization value q_(i,j) is predicted, and it isnormalized with an appropriate scale for approximation. (There is nocondition for the scale.)

For example, when assuming that digital watermark data is read fromwatermarked motion pictures which are MPEG compressed, the distributionshown in FIG. 30 can be approximated by a Laplacian distribution. Thus,a Laplacian distribution of average 0 and variance 0.08 or a normaldistribution of average 0 and variance 1/16 can be used effectively asthe weighting function.

In addition, there is another method which uses another distributionfunction. The distribution function is formed so as to predict the errorof the watermarked content data.

The digital watermark reading apparatus 106 reconstitutes and outputsdigital watermark data {tilde over (w)}₀,{tilde over (w)}₁, . . .,{tilde over (w)}_(n-1) from read watermark sequence by applying, forexample, $W_{i} = \{ \begin{matrix}1 & {{\sum\limits_{j = 0}^{m - 1}\quad{\overset{\_}{w}}_{i,j}} \geq 0} & \quad \\{- 1} & {{\sum\limits_{j = 0}^{m - 1}\quad{\overset{\_}{w}}_{i,j}} < 0} & \quad\end{matrix} $or Japanese patent-application No.10-219236, “Embedding data codingmethod, the apparatus, computer readable medium storing embedding datacoding program, read data decoding method, the apparatus, computerreadable medium storing read data decoding program, digital watermarkdata coding method, the apparatus, computer readable medium storingdigital watermark coding program, digital watermark decoding method, theapparatus, computer readable medium storing digital watermark decodingprogram”.

In addition, the above-mentioned process performed by the digitalwatermark reading apparatus 106 can be constructed by a programwhich-can be stored in a computer readable medium such as a disk unit, afloppy disk, CD-ROM and the like. That is, by installing the program ina computer such as one shown in FIG. 17, the processes of watermarkreading of the present invention can be carried out. In addition, thedigital watermark reading apparatus of the present invention can berealized by the integrated circuit shown in FIG. 18.

Experiments is performed in order to compare the method of the presentinvention and the conventional method of digital watermarking to motionpictures described in Japanese patent application No.9-164466.

As experimental conditions, a unit for digital watermark processing isassumed to be a 16×16 pixel and the conventional digital watermark datasequence reading is assumed to be {tilde over (w)}_(i,j)=(n_(i,j) mod2)×2−1 on the basis of the assumptions of the above-mentionedembodiment. Watermark data is reconstituted as {tilde over (w)}₀w₁, . .. ,w_(n-1) for both of the present invention and the conventionalmethod.

As shown in FIG. 34, it is recognized that digital watermark datareading success rate is improved in an MPEG-1 coded picture in any bitrates. The result shows the effectiveness of the present invention.Here, the digital watermark data reading success rate is obtained bydividing the number of correctly reconstituted digital watermark data bythe total number of embedded digital watermark data.

According to the present invention, the digital watermark data sequenceis separated from the noise so that error bits which are included in thedigital watermark data sequence can be reduced, thereby the digitalwatermark data reading success rate is improved in comparison with theconventional method.

In addition, since weights are assigned to the digital watermark datasequence, the present invention is especially effective when therepeating number of watermark embedding is small.

The point of the present invention corresponding to the third objectiveis applying soft decisions for the digital watermark reading process asopposed to the conventional method which uses hard decisions. Thepresent invention is not limited to the above-mentioned process and canapply to other equivalent digital watermarking method.

In the above-mentioned embodiments corresponding to first-third objects,embodiments corresponding to each object can be performed withembodiments corresponding to other objects.

The present invention is not limited to the specifically disclosedembodiments, and variations and modifications may be made withoutdeparting from the scope of the invention.

1. A method for embedding digital watermark data in digital datacontents, said method comprising the steps of: receiving said digitaldata contents and said digital watermark data; dividing said digitaldata contents into block data; obtaining a frequency coefficient of saidblock data; obtaining a complexity of said block data; obtaining anamount of transformation of said frequency coefficient from saidcomplexity and said digital watermark data by using a quantizationwidth; embedding said digital watermark data in said digital datacontents by transforming said frequency coefficient by said amount; andgenerating watermarked digital data contents.
 2. The method as claimedin claim 1, said step of obtaining said complexity of said block datacomprising the steps of transforming said block data, by applying awavelet transform, into coefficients of said wavelet transform, andobtaining said complexity on the basis of the number of high frequencycoefficients in said coefficients of said wavelet transform, each ofsaid high frequency coefficients exceeding a threshold.
 3. A method forembedding digital watermark data in digital data contents, said methodcomprising the steps of: receiving said digital data contents and saiddigital watermark data; dividing said digital data contents into blockdata; obtaining a frequency coefficient of said block data; obtaining acomplexity of said block data; obtaining an amount of transformation ofsaid frequency coefficient from said digital watermark data by using aquantization width corresponding to said frequency coefficient, saidquantization width being obtained beforehand according to a manipulationmethod of said digital data contents; embedding said digital watermarkdata in said digital data contents by transforming said frequencycoefficient by said amount; and generating watermarked digital datacontents.
 4. The method as claimed in claim 3, wherein said quantizationwidth is obtained by a method comprising the steps of: dividing firstdigital data contents into one or a plurality of first block data;dividing second digital data contents into one or a plurality of secondblock data, said second digital data contents being obtained bymanipulating said first digital data contents with a predeterminedmanipulation method; transforming said first block data and said secondblock data into first frequency coefficients and second frequencycoefficients respectively by applying an orthogonal transform; obtainingdifference values between said first frequency coefficients and saidsecond frequency coefficients for each frequency coefficient;calculating a standard deviation of distribution of said differencevalues; and obtaining said quantization width by multiplying saidstandard deviation by a watermark embedding strength.
 5. A method forreading digital watermark data embedded in digital data contents, saidmethod comprising the steps of: receiving said digital data contents;dividing said digital data contents into block data; obtaining afrequency coefficient of said block data; and generating digitalwatermark data from said frequency coefficient by using a quantizationwidth corresponding to said frequency coefficient, said quantizationwidth being obtained beforehand according to a manipulation method ofsaid digital data contents.
 6. The method as claimed in claim 5, whereinsaid quantization width is obtained by a method comprising the steps of:dividing first digital data contents into one or a plurality of firstblock data; dividing second digital data contents into one or aplurality of second block data, said second digital data contents beingobtained by manipulating said first digital data contents with apredetermined manipulation method; transforming said first block dataand said second block data into first frequency coefficients and secondfrequency coefficients respectively by applying an orthogonal transform;obtaining difference values between said first frequency coefficientsand said second frequency coefficients for each frequency coefficient;calculating a standard deviation of distribution of said differencevalues; and obtaining said quantization width by multiplying saidstandard deviation by a watermark embedding strength.
 7. An apparatusfor embedding digital watermark data in digital data contents, saidapparatus comprising: means for receiving said digital data contents andsaid digital watermark data; means for dividing said digital datacontents into block data; means for obtaining a frequency coefficient ofsaid block data; means for obtaining a complexity of said block data;means for obtaining an amount of transformation of said frequencycoefficient from said complexity and said digital watermark data byusing a quantization width; means for embedding said digital watermarkdata in said digital data contents by transforming said frequencycoefficient by said amount; and means for generating watermarked digitaldata contents.
 8. The apparatus as claimed in claim 7, said means forobtaining said complexity of said block data comprising: means fortransforming said block data, by applying a wavelet transform, intocoefficients of said wavelet transform, and means for obtaining saidcomplexity on the basis of the number of high frequency coefficients insaid coefficients of said wavelet transform, each of said high frequencycoefficients exceeding a threshold.
 9. An apparatus for embeddingdigital watermark data in digital data contents, said apparatuscomprising: means for receiving said digital data contents and saiddigital watermark data; means for dividing said digital data contentsinto block data; means for obtaining a frequency coefficient of saidblock data; means for obtaining a complexity of said block data; meansfor obtaining an amount of transformation of said frequency coefficientfrom said digital watermark data by using a quantization widthcorresponding to said frequency coefficient, said quantization widthbeing obtained beforehand according to a manipulation method of saiddigital data contents; means for embedding said digital watermark datain said digital data contents by transforming said frequency coefficientby said amount; and means for generating watermarked digital datacontents.
 10. The apparatus as claimed in claim 9, wherein saidquantization width is obtained by means comprising: means for dividingfirst digital data contents into one or a plurality of first block data;means for dividing second digital data contents into one or a pluralityof second block data, said second digital data contents being obtainedby manipulating said first digital data contents with a predeterminedmanipulation method; means for transforming said first block data andsaid second block data into first frequency coefficients and secondfrequency coefficients respectively by applying an orthogonal transform;means for obtaining difference values between said first frequencycoefficients and said second frequency coefficients for each frequencycoefficient; means for calculating a standard deviation of distributionof said difference values; and means for obtaining said quantizationwidth by multiplying said standard deviation by a watermark embeddingstrength.
 11. An apparatus for reading digital watermark data embeddedin digital data contents, said apparatus comprising: means for receivingsaid digital data contents; means for dividing said digital datacontents into block data; means for obtaining a frequency coefficient ofsaid block data; and means for generating digital watermark data fromsaid frequency coefficient by using a quantization width correspondingto said frequency coefficient, said quantization width being obtainedbeforehand according to a manipulation method of said digital datacontents.
 12. The apparatus as claimed in claim 11, wherein saidquantization width is obtained by means comprising: means for dividingfirst digital data contents into one or a plurality of first block data;means for dividing second digital data contents into one or a pluralityof second block data, said second digital data contents being obtainedby manipulating said first digital data contents with a predeterminedmanipulation method; means for transforming said first block data andsaid second block data into first frequency coefficients and secondfrequency coefficients respectively by applying an orthogonal transform;means for obtaining difference values between said first frequencycoefficients and said second frequency coefficients for each frequencycoefficient; means for calculating a standard deviation of distributionof said difference values; and means for obtaining said quantizationwidth by multiplying said standard deviation by a watermark embeddingstrength.
 13. An integrated circuit for embedding digital watermark datain digital data contents, said integrated circuit comprising: means forreceiving said digital data contents and said digital watermark data;means for dividing said digital data contents into block data; means forobtaining a frequency coefficient of said block data; means forobtaining a complexity of said block data; means for obtaining an amountof transformation of said frequency coefficient from said complexity andsaid digital watermark data by using a quantization width; means forembedding said digital watermark data in said digital data contents bytransforming said frequency coefficient by said amount; and means forgenerating watermarked digital data contents.
 14. The integrated circuitas claimed in claim 13, said means for obtaining said complexity of saidblock data comprising: means for transforming said block data, byapplying a wavelet transform, into coefficients of said wavelettransform, and means for obtaining said complexity on the basis of thenumber of high frequency coefficients in said coefficients of saidwavelet transform, each of said high frequency coefficients exceeding athreshold.
 15. An integrated circuit for embedding digital watermarkdata in digital data contents, said integrated circuit comprising: meansfor receiving said digital data contents and said digital watermarkdata, means for dividing said digital data contents into block data;means for obtaining a frequency coefficient of said block data; meansfor obtaining a complexity of said block data; means for obtaining anamount of transformation of said frequency coefficient from said digitalwatermark data by using a quantization width corresponding to saidfrequency coefficient, said quantization width being obtained beforehandaccording to a manipulation method of said digital data contents; meansfor embedding said digital watermark data in said digital data contentsby transforming said frequency coefficient by said amount; and means forgenerating watermarked digital data contents.
 16. The integrated circuitas claimed in claim 15, wherein said quantization width is obtained bymeans comprising: means for dividing first digital data contents intoone or a plurality of first block data; means for dividing seconddigital data contents into one or a plurality of second block data, saidsecond digital data contents being obtained by manipulating said firstdigital data contents with a predetermined manipulation method; meansfor transforming said first block data and said second block data intofirst frequency coefficients and second frequency coefficientsrespectively by applying an orthogonal transform; means for obtainingdifference values between said first frequency coefficients and saidsecond frequency coefficients for each frequency coefficient; means forcalculating a standard deviation of distribution of said differencevalues; and means for obtaining said quantization width by multiplyingsaid standard deviation by a watermark embedding strength.
 17. Anintegrated circuit for reading digital watermark data embedded indigital data contents, said integrated circuit comprising: means forreceiving said digital data contents; means for dividing said digitaldata contents into block data; means for obtaining a frequencycoefficient of said block data; and means for generating digitalwatermark data from said frequency coefficient by using a quantizationwidth corresponding to said frequency coefficient, said quantizationwidth being obtained beforehand according to a manipulation method ofsaid digital data contents.
 18. The integrated circuit as claimed inclaim 17, wherein said quantization width is obtained by meanscomprising: means for dividing first digital data contents into one or aplurality of first block data; means for dividing second digital datacontents into one or a plurality of second block data, said seconddigital data contents being obtained by manipulating said first digitaldata contents with a predetermined manipulation method; means fortransforming said first block data and said second block data into firstfrequency coefficients and second frequency coefficients respectively byapplying an orthogonal transform; means for obtaining difference valuesbetween said first frequency coefficients and said second frequencycoefficients for each frequency coefficient; means for calculating astandard deviation of distribution of said difference values; and meansfor obtaining said quantization width by multiplying said standarddeviation by a watermark embedding strength.
 19. A computer readablemedium storing program code for causing a computer system to embeddigital watermark data in digital data contents, said computer readablemedium comprising: program code means for receiving said digital datacontents and said digital watermark data; program code means fordividing said digital data contents into block data; program code meansfor obtaining a frequency coefficient of said block data; program codemeans for obtaining a complexity of said block data; program code meansfor obtaining an amount of transformation of said frequency coefficientfrom said complexity and said digital watermark data by using aquantization width; program code means for embedding said digitalwatermark data in said digital data contents by transforming saidfrequency coefficient by said amount; and program code means forgenerating watermarked digital data contents.
 20. The computer readablemedium as claimed in claim 19, said program code means for obtainingsaid complexity of said block data comprising: program code means fortransforming said block data, by applying a wavelet transform, intocoefficients of said wavelet transform, and program code means forobtaining said complexity on the basis of the number of high frequencycoefficients in said coefficients of said wavelet transform, each ofsaid high frequency coefficients exceeding a threshold.
 21. A computerreadable medium storing program code for causing a computer system toembed digital watermark data in digital data contents, said computerreadable medium comprising: program code means for receiving saiddigital data contents and said digital watermark data; program codemeans for dividing said digital data contents into block data; programcode means for obtaining a frequency coefficient of said block data;program code means for obtaining a complexity of said block data;program code means for obtaining an amount of transformation of saidfrequency coefficient from said digital watermark data by using aquantization width corresponding to said frequency coefficient, saidquantization width being obtained beforehand according to a manipulationmethod of said digital data contents; program code means for embeddingsaid digital watermark data in said digital data contents bytransforming said frequency coefficient by said amount; and program codemeans for generating watermarked digital data contents.
 22. The computerreadable medium as claimed in claim 21, wherein said quantization widthis obtained by means comprising: program code means for dividing firstdigital data contents into one or a plurality of first block data;program code means for dividing second digital data contents into one ora plurality of second block data, said second digital data contentsbeing obtained by manipulating said first digital data contents with apredetermined manipulation method; program code means for transformingsaid first block data and said second block data into first frequencycoefficients and second frequency coefficients respectively by applyingan orthogonal transform; program code means for obtaining differencevalues between said first frequency coefficients and said secondfrequency coefficients for each frequency coefficient; program codemeans for calculating a standard deviation of distribution of saiddifference values; and program code means for obtaining saidquantization width by multiplying said standard deviation by a watermarkembedding strength.
 23. A computer readable medium storing program codefor causing a computer system to embed digital watermark data in digitaldata contents, said computer readable medium comprising: program codemeans for receiving said digital data contents; program code means fordividing said digital data contents into block data; program code meansfor obtaining a frequency coefficient of said block data; and programcode means for generating digital watermark data from said frequencycoefficient by using a quantization width corresponding to saidfrequency coefficient, said quantization width being obtained beforehandaccording to a manipulation method of said digital data contents. 24.The computer readable medium as claimed in claim 23, wherein saidquantization width is obtained by means comprising: program code meansfor dividing first digital data contents into one or a plurality offirst block data; program code means for dividing second digital datacontents into one or a plurality of second block data, said seconddigital data contents being obtained by manipulating said first digitaldata contents with a predetermined manipulation method; program codemeans for transforming said first block data and said second block datainto first frequency coefficients and second frequency coefficientsrespectively by applying an orthogonal transform; program code means forobtaining difference values between said first frequency coefficientsand said second frequency coefficients for each frequency coefficient;program code means for calculating a standard deviation of distributionof said difference values; and program code means for obtaining saidquantization width by multiplying said standard deviation by a watermarkembedding strength. 25-72. (canceled)